Update CBMC dependency to 6.10.0

[tautschnig]

Upgrading to 6.9.0 requires changes as described below. Upgrading from 6.9.0 to 6.10.0 does not require any further changes.

Changes in CBMC's set of static objects require retuning shadow-memory object-count test: The unsupported_num_objects test depends on CBMC's internal object-ID numbering: it creates N objects and expects the (N+k)-th object's ID to cross Kani's 1024-object shadow-memory limit. Newer CBMC allocates one fewer auxiliary object, so the previous N values (1019 pass / 1020 fail) no longer straddle the limit -- the fail harness verified successfully instead of failing.

Bump the thresholds by one (1020 pass / 1021 fail) to restore the boundary, update the explanatory comment, and note that these counts are sensitive to CBMC's object numbering and may need adjusting on future CBMC upgrades.

CBMC 6.10 makes the slow harness's Display/to_string formatting path far more memory-heavy: the original "foo"/unwind(6) version peaks at ~26 GB with Kani's default Cadical solver and deterministically OOM-kills the 16 GB GitHub-hosted perf runner ("runner has received a shutdown signal"). No solver is both under 16 GB and fast enough (minisat2/kissat stay ~8 GB but do not finish in >15 min), so the harness itself must shrink.

Use an empty payload (formatted result "A.") and unwind(3) -- the smallest bound that still fully unrolls the formatting loops. This keeps peak memory to ~11 GB while still exercising the trait/formatting path the test guards. Both harnesses verify successfully.

Resolves: #4605
Resolves: #4617

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[Copilot]

Pull request overview

This PR updates Kani’s pinned CBMC version to 6.10.0 and adjusts a shadow-memory boundary test whose expected behavior depends on CBMC’s internal object-ID numbering (static object count changed in newer CBMC).

Changes:

• Bump CBMC dependency metadata from 6.8.0 to 6.10.0.
• Retune unsupported_num_objects thresholds to re-establish a pass/fail boundary at Kani’s 1024-object shadow-memory limit.
• Improve the test’s explanatory comments to warn that the thresholds may need future adjustment on CBMC upgrades.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
tests/expected/shadow/unsupported_num_objects/test.rs	Updates object-ID accounting comments and shifts the pass/fail N thresholds by +1 to match CBMC’s new auxiliary-object behavior.
kani-dependencies	Pins CBMC to version 6.10.0 (minor 10).

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[tautschnig]

We need to investigate why CBMC's brew releases are no longer fully working.