feat: add srt builtin — sort lists and text

[danieljohnmorris]

Summary

• Adds srt builtin that sorts lists (of numbers or text) and text strings (by character)
• Implemented across verifier, tree-walk interpreter, and bytecode VM
• Lists must be homogeneous (all numbers or all text); mixed lists produce a runtime error
• Text strings are sorted by character (e.g. srt "cab" returns "abc")

Test plan

• Verifier: accepts srt with list arg, rejects wrong type (ILO-T013)
• Interpreter: sort number list, sort text list, sort text string
• VM: sort number list, sort text list
• All 858 tests pass
• Clippy clean (no new warnings)

[danieljohnmorris]

Superseded by #56 which combines all builtins + ternary with correct opcode numbering.