Centralize skill invocation helpers in codex-skills (#37174)

## What changed

- Move tool mention parsing, skill-name counting, and implicit invocation detection into `codex-skills` and expose them through its public API.
- Decouple implicit invocation detection from `SkillLoadOutcome` with an `ImplicitSkillLookup` trait, while preserving the existing `core-skills` interface through re-exports.
- Cover remote plugin attribution for both implicit `SKILL.md` reads and skill script runs.

GitOrigin-RevId: f3da85c9821868638ccfd2fc2e01e0869d2fd437

codex-rs/skills/Cargo.toml

@@ -15,11 +15,13 @@ workspace = true
 
 [dependencies]
 codex-protocol = { workspace = true }
+codex-shell-command = { workspace = true }
 codex-utils-absolute-path = { workspace = true }
 codex-utils-path-uri = { workspace = true }
 include_dir = { workspace = true }
 serde = { workspace = true, features = ["derive"] }
 serde_yaml = { workspace = true }
+shlex = { workspace = true }
 thiserror = { workspace = true }
 tracing = { workspace = true }