codex-tools: extract shared tool schema parsing

[bolinfest]

Why

parse_tool_input_schema and the supporting JsonSchema model were living in core/src/tools/spec.rs, but they already serve callers outside codex-core.

Keeping that shared schema parsing logic inside codex-core makes the crate boundary harder to reason about and works against the guidance in AGENTS.md to avoid growing codex-core when reusable code can live elsewhere.

This change takes the first extraction step by moving the schema parsing primitive into its own crate while keeping the rest of the tool-spec assembly in codex-core.

What changed

• added a new codex-tools crate under codex-rs/tools
• moved the shared tool input schema model and sanitizer/parser into tools/src/json_schema.rs
• kept tools/src/lib.rs exports-only, with the module-level unit tests split into json_schema_tests.rs
• updated codex-core to use codex-tools::JsonSchema and re-export parse_tool_input_schema
• updated codex-app-server dynamic tool validation to depend on codex-tools directly instead of reaching through codex-core
• wired the new crate into the Cargo workspace and Bazel build graph