feat(openai): wire per-call response_format and tool strict knobs thr…

[Sizolity]

What

Add two narrowly-scoped, fully-typed knobs to libs/acl/openai so callers can use OpenAI / OpenAI-compatible Structured Outputs features per-call, without dropping to untyped WithExtraFields workarounds or WithRequestPayloadModifier post-hoc JSON patching.

1. WithResponseFormat(*ChatCompletionResponseFormat) model.Option — per-call counterpart of Config.ResponseFormat. Per-call value takes precedence over config; not supplying it preserves existing fallback behavior.
2. ToolInfoExtraKeyStrict constant — opt a single tool into Structured Outputs strict mode via schema.ToolInfo.Extra[openai.ToolInfoExtraKeyStrict] = true. Non-bool values are silently ignored.
   Both implement what the existing libs/acl/openai/README.md already documents (Available call options → openai.WithResponseFormat(format); "JSON Schema Response" example referencing strict tools) but which currently has no working code path.

Why

Closes #856.
A common pattern is a single shared ChatModel that serves two kinds of calls:

• A structured-extraction call that needs response_format: {\"type\":\"json_object\"} (or json_schema) so the server guarantees a syntactically valid JSON body.
• A free-form text call on the same model that must NOT have response_format set.
  For tool calls, opt-in strict: true solves a parallel issue: without it, providers occasionally emit syntactically invalid JSON in tool-call arguments — including unescaped control bytes inside string values — which strict JSON parsers reject with errors like Syntax error at index N: invalid char.
  Today neither knob has a per-call switch via the typed API surface. See [openai] Structured-output knobs not wired through: WithResponseFormat (documented but missing) and FunctionDefinition.Strict (dropped during marshal) #856 for the full evidence trail.

Scope

This PR only touches libs/acl/openai:

File	Change
option.go	Add ResponseFormat field to openaiOptions; add WithResponseFormat setter; add ToolInfoExtraKeyStrict constant.
chat_model.go	In genRequest, prefer specOptions.ResponseFormat over c.config.ResponseFormat. In toTools, read ti.Extra[ToolInfoExtraKeyStrict] as bool. In tool marshal site, propagate t.Function.Strict to openai.FunctionDefinition.Strict.
tool.go	Add Strict bool to internal functionDefinition.
chat_model_test.go	6 new subtests under Test_genRequest.
option_test.go	Setter test matching the existing pattern.
Design choice for the Strict knob: sourced via schema.ToolInfo.Extra (option 3 in #856's "Proposed direction (b)"). This keeps the change inside libs/acl/openai and does NOT require modifying cloudwego/eino core — schema.ToolInfo's public API is unchanged. If the team later prefers a typed field on schema.ToolInfo.Function, migrating is a one-line change to toTools.
Following the repo's convention (see #847), the matching re-export in components/model/openai/option.go for WithResponseFormat is left to a follow-up bump PR once a new libs/acl/openai is tagged. The ToolInfoExtraKeyStrict constant is already accessible to wrapper users by importing libs/acl/openai directly.

Tests

```
GOTOOLCHAIN=go1.24.4 MOCKEY_CHECK_GCFLAGS=false \
go test -count=1 -gcflags='all=-N -l' ./libs/acl/openai/...
ok github.com/cloudwego/eino-ext/libs/acl/openai
```
New subtests under Test_genRequest:

• WithResponseFormat sets format when config has none
• WithResponseFormat overrides Config.ResponseFormat (including JSONSchema + Strict round-trip)
• no WithResponseFormat falls back to Config.ResponseFormat (regression pin)
• ToolInfo.Extra openai_strict=true propagates to FunctionDefinition.Strict
• tool without Extra leaves Strict=false
• non-bool openai_strict in Extra is silently ignored
  Plus Test_OpenAIOptions_Setters/WithResponseFormat.

Backwards compatibility

All existing tests pass unchanged. Tools without Extra have Strict=false (pre-PR behavior). Calls without WithResponseFormat fall through to the prior Config.ResponseFormat path.
Closes #856.

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