patina_boot: Build on the stable toolchain

[kat-perez]

Summary

patina_boot pinned a nightly toolchain for two features. Neither is necessary, and the
pin actively prevented the crate from being used for its intended purpose.

• never_type — the Result<!, EfiError> signatures become
  Result<core::convert::Infallible, EfiError>. This carries the same meaning here: every
  implementation and every caller either returns an error or diverges, so nothing ever
  constructs the success value.
• coverage_attribute — now gated behind cfg(coverage)
  (#![cfg_attr(coverage, feature(coverage_attribute))] /
  #[cfg_attr(coverage, coverage(off))]), matching every upstream Patina crate. Coverage
  runs still opt in by adding the feature through RUSTFLAGS, so the #[coverage(off)]
  annotations keep working where they matter.

One unstable feature remains, and it is not ours: the patina SDK enables allocator_api
whenever alloc or test is active. Patina's own answer to that is to unlock it on a
pinned stable channel via RUSTC_BOOTSTRAP, restricted to the features Patina has
accepted through its unstable feature process. This PR adopts that same configuration, so
patina_boot is now built the same way as the rest of the ecosystem.

Why this matters

This is not a cleanup. Patina DXE core repositories set
-Z allow-features=c_variadic,allocator_api, which is an allowlist — it restricts what
RUSTC_BOOTSTRAP unlocks. never_type and coverage_attribute are not on it, so adding
patina_boot as a dependency of a DXE core failed to compile outright:

error[E0725]: the feature `coverage_attribute` is not in the list of allowed features
error[E0725]: the feature `never_type` is not in the list of allowed features

In other words, patina_boot could not be consumed by the thing it exists to run inside of.
After this change, a local prototype DXE core with BootDispatcher registered as a
component builds cleanly against the crate.

Changes

File	Change
src/lib.rs	Drop feature(never_type); gate coverage_attribute on cfg(coverage)
src/boot_orchestrator.rs, src/boot_dispatcher.rs, src/orchestrators/simple_boot_manager.rs	Result<!, _> → Result<Infallible, _>
src/boot_dispatcher.rs, src/helpers.rs, src/orchestrators/simple_boot_manager.rs	#[coverage(off)] → #[cfg_attr(coverage, coverage(off))]
.cargo/config.toml	New. RUSTC_BOOTSTRAP + accepted-feature allowlist, mirroring upstream Patina
Cargo.toml	Declare cfg(coverage) via unexpected_cfgs check-cfg
rust-toolchain.toml	nightly-2026-02-27 → 1.95.0
.github/workflows/uefi-check.yml	Same channel change for the patina_boot job, and correct the header comment

patina_tianocore still pins nightly-2025-12-12 and is untouched here.

Validation

Ran CI's exact commands on stable 1.95.0, all passing with zero warnings:

• cargo fmt --check
• cargo clippy --all-features -- -D warnings (host, x86_64-unknown-uefi, aarch64-unknown-uefi)
• cargo doc --no-deps with RUSTDOCFLAGS=-D warnings
• cargo build for both UEFI targets
• cargo test — 94 unit tests, 6 doctests
• cargo build --benches

Behaviour is unchanged; this is a compile-time and toolchain change only.

[Copilot]

🟢 Approval recommended

The changes are primarily toolchain/configuration and type/attribute substitutions with a single minor documentation consistency nit noted.

Pull request overview

This PR updates uefi/crates/patina_boot to build on a pinned stable Rust toolchain by removing the crate-owned nightly feature requirements, gating coverage-only attributes behind cfg(coverage), and adopting Patina’s stable RUSTC_BOOTSTRAP + -Z allow-features configuration so the crate can be consumed by Patina DXE cores.

Changes:

• Switch patina_boot from nightly to stable 1.95.0 (crate toolchain pin + CI job toolchain).
• Replace Result<!, EfiError> with Result<core::convert::Infallible, EfiError> and gate #[coverage(off)] behind cfg(coverage).
• Add per-crate Cargo configuration to enable RUSTC_BOOTSTRAP with an accepted-feature allowlist; declare cfg(coverage) to avoid unexpected_cfgs warnings.

File summaries

File	Description
uefi/crates/patina_boot/src/orchestrators/simple_boot_manager.rs	Switches ! to Infallible and gates coverage attributes.
uefi/crates/patina_boot/src/lib.rs	Drops nightly-only feature requirements; gates coverage_attribute behind cfg(coverage).
uefi/crates/patina_boot/src/helpers.rs	Gates #[coverage(off)] behind cfg(coverage).
uefi/crates/patina_boot/src/boot_orchestrator.rs	Updates trait signature to Infallible (doc wording needs a small follow-up).
uefi/crates/patina_boot/src/boot_dispatcher.rs	Gates coverage attributes; updates test trait impl return type to Infallible.
uefi/crates/patina_boot/rust-toolchain.toml	Pins stable toolchain 1.95.0.
uefi/crates/patina_boot/Cargo.toml	Declares cfg(coverage) for unexpected_cfgs lint checking.
uefi/crates/patina_boot/.cargo/config.toml	Adds RUSTC_BOOTSTRAP + -Z allow-features configuration for stable builds.
.github/workflows/uefi-check.yml	Updates CI toolchain for patina_boot job to stable and refreshes header comment.

Review details

• Files reviewed: 9/9 changed files
• Comments generated: 1
• Review effort level: Lite

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[Copilot]

🟢 Approval recommended

The changes are narrowly scoped to toolchain/configuration and mechanical type/attribute gating updates, with no functional behavior changes introduced.

Review details

• Files reviewed: 9/9 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🟢 Approval recommended

The changes are cohesive and self-consistent (API/doc updates, coverage gating, toolchain/CI alignment) with no verified correctness issues found in the modified regions.

Review details

• Files reviewed: 9/9 changed files
• Comments generated: 0 new
• Review effort level: Lite