codex-tools: extract configured tool specs

[bolinfest]

Why

This continues the codex-tools migration by moving another passive tool-spec layer out of codex-core.

After ToolSpec moved into codex-tools, codex-core still owned ConfiguredToolSpec and create_tools_json_for_responses_api(). Both are data-model and serialization helpers rather than runtime orchestration, so keeping them in core/src/tools/registry.rs and core/src/tools/spec.rs left passive tool-definition code coupled to codex-core longer than necessary.

What changed

• moved ConfiguredToolSpec into codex-rs/tools/src/tool_spec.rs
• moved create_tools_json_for_responses_api() into codex-rs/tools/src/tool_spec.rs
• re-exported the new surface from codex-rs/tools/src/lib.rs, which remains exports-only
• updated core/src/client.rs, core/src/tools/registry.rs, and core/src/tools/router.rs to consume the extracted types and serializer from codex-tools
• moved the tool-list serialization test into codex-rs/tools/src/tool_spec_tests.rs
• added focused unit coverage for ConfiguredToolSpec::name()
• simplified core/src/tools/spec_tests.rs to use the extracted ConfiguredToolSpec::name() directly and removed the now-redundant local tool_name() helper
• updated codex-rs/tools/README.md so the crate boundary reflects the newly extracted tool-spec wrapper and serialization helper

Test plan

• cargo test -p codex-tools
• CARGO_TARGET_DIR=/tmp/codex-core-configured-spec cargo test -p codex-core --lib tools::spec::
• CARGO_TARGET_DIR=/tmp/codex-core-configured-spec cargo test -p codex-core --lib client::
• just fix -p codex-tools -p codex-core
• just argument-comment-lint

References

• codex-tools: extract shared tool schema parsing #15923
• codex-tools: extract MCP schema adapters #15928
• codex-tools: extract dynamic tool adapters #15944
• codex-tools: introduce named tool definitions #15953
• codex-tools: extract responses API tool models #16031
• codex-tools: extract tool spec models #16047