feat: add cross-provider tool call ID compatibility

[mikehostetler]

Summary

• add a framework-level engine to normalize/validate tool call IDs across provider switches
• add generation option () and provider callback
• wire provider-specific policies for Anthropic-family, Bedrock Converse, and Vertex Gemini/Claude paths
• enforce local unresolved-tool-turn validation for strict providers
• add provider and compat tests plus a simplified live integration test for OpenAI -> Anthropic

Implementation Notes

• constrained providers sanitize/reject as needed; OpenAI-compatible providers default to passthrough
• Gemini body handling now uses shared policy plumbing to drop
• Bedrock Converse applies sanitize + 64-char max ID handling

Tests

• Compiling 17 files (.ex)
  Generated req_llm app
  Running ExUnit with seed: 103226, max_cases: 20
  Excluding tags: [:coverage, :integration]

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Finished in 0.3 seconds (0.3s async, 0.03s sync)
161 tests, 0 failures

• Running ExUnit with seed: 716380, max_cases: 20
  Including tags: [:coverage, :integration]

...
Finished in 3.0 seconds (0.00s async, 3.0s sync)
3 tests, 0 failures

[mikehostetler]

Thanks for pushing this large change through. I'm adding needs_work because CI is currently failing on this branch.

The failing jobs are in Test / Elixir 1.18 and Test / Elixir 1.19 with FunctionClauseError in ReqLLM.Providers.GoogleVertex.get_model_family/1 (seen from test/providers/google_vertex_gemini_test.exs).

Please address the failing path and re-run CI; once tests are green, this can move forward.