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/Cargo.lock

@@ -2917,7 +2917,6 @@ dependencies = [
  "codex-model-provider",
  "codex-otel",
  "codex-protocol",
- "codex-shell-command",
  "codex-skills",
  "codex-utils-absolute-path",
  "codex-utils-path-uri",
@@ -2929,7 +2928,6 @@ dependencies = [
  "serde",
  "serde_json",
  "serde_yaml",
- "shlex",
  "tempfile",
  "tokio",
  "toml 0.9.11+spec-1.1.0",
@@ -4086,12 +4084,14 @@ name = "codex-skills"
 version = "0.0.0"
 dependencies = [
  "codex-protocol",
+ "codex-shell-command",
  "codex-utils-absolute-path",
  "codex-utils-path-uri",
  "include_dir",
  "pretty_assertions",
  "serde",
  "serde_yaml",
+ "shlex",
  "thiserror 2.0.18",
  "tracing",
 ]