codex-tools: extract shared tool schema parsing (#15923)

## 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

codex-rs/Cargo.toml

@@ -51,6 +51,7 @@ members = [
     "otel",
     "tui",
     "tui_app_server",
+    "tools",
     "v8-poc",
     "utils/absolute-path",
     "utils/cargo-bin",
@@ -150,6 +151,7 @@ codex-skills = { path = "skills" }
 codex-state = { path = "state" }
 codex-stdio-to-uds = { path = "stdio-to-uds" }
 codex-terminal-detection = { path = "terminal-detection" }
+codex-tools = { path = "tools" }
 codex-tui = { path = "tui" }
 codex-tui-app-server = { path = "tui_app_server" }
 codex-v8-poc = { path = "v8-poc" }