Document optional return types for array pop/shift/at

[ATX24]

Summary

• update the Array methods section in plugins/baml/skills/core/SKILL.md
• annotate optional-returning methods with explicit signatures:
  • pop() -> T?
  • shift() -> T?
  • at(i: int) -> T?
• clarify null-case behavior for each method
• add an idiomatic ?? unwrap snippet covering pop/shift/at
• distinguish void-returning mutators (push, unshift) from optional-returning reads/removals

Validation

• checked repository layout for build/test configs (no package.json, Makefile, or baml.toml targets present)
• ran git diff --check (clean)

CodeRabbit

• @coderabbitai review