Add GOTO and BREAK control statements to TP2

[4Luke4]

Summary

This adds first-class GOTO, labels, and BREAK statements to both TP2 action and patch code.

OUTER_SET attempts = 0

::retry::
OUTER_SET attempts += 1

ACTION_IF attempts < 3 BEGIN
  GOTO retry
END

OUTER_WHILE 1 BEGIN
  BREAK
END

The scope model takes inspiration from Lua's control statements, while being adapted to WeiDU's action/patch execution model.

Syntax and semantics

• ::label:: declares a label.
• GOTO label resumes execution immediately after a visible label.
• BREAK exits the innermost supported loop.
• Labels are non-empty, case-sensitive literal names; they are not evaluated as variables.
• Action and patch labels occupy separate namespaces.
• A label is visible in its declaring list and nested same-domain structural lists.
• A jump may leave a nested conditional or loop, but cannot jump into one.
• Functions, macros, included files, opposite-domain embedded code, and separate-buffer patch bodies form control-flow boundaries.
• ACTION_TRY and PATCH_TRY do not intercept control transfers.
• Patch mutations are preserved when a patch GOTO or BREAK leaves a nested block.
• BREAK exits the innermost:
  • action OUTER_WHILE, OUTER_FOR, ACTION_FOR_EACH, ACTION_PHP_EACH, or ACTION_BASH_FOR;
  • patch WHILE, FOR, PATCH_FOR_EACH, PATCH_PHP_EACH, or PATCH_BASH_FOR.
• OUTER_FOR and FOR do not execute their increment lists after BREAK.

WeiDU validates the complete control-flow structure during parsing. It rejects:

• undefined targets;
• duplicate visible labels;
• empty labels;
• jumps into nested blocks;
• cross-domain jumps;
• jumps across macro/function/include boundaries;
• BREAK outside a supported loop.

Diagnostics include the source filename, line, and column.

Implementation

• Adds source-located action and patch AST nodes for labels, GOTO, and BREAK.
• Introduces a dedicated static control-flow validator.
• Uses cached label maps for constant-time target lookup.
• Retains a fast path for lists without labels.
• Uses an explicit program counter for stack-safe backward jumps.
• Carries the current patch buffer through non-local patch control transfers.
• Preserves scope and iteration-variable cleanup during transfers.
• Keeps the size-constrained legacy parser unchanged by using WeiDU's existing fallback to the Elkhound grammar for the new productions.

Tests

A new make test-control-statements target covers:

• forward and backward action and patch jumps;
• jumps leaving nested loops;
• patch-buffer preservation;
• ACTION_TRY, PATCH_TRY, WITH_SCOPE, and PATCH_WITH_SCOPE;
• all supported action and patch loop forms;
• innermost-loop BREAK selection;
• exact diagnostics for every invalid scope or target case.

A temporary branch-only workflow built the Linux executable using the repository's archived OCaml 4.08.1 unsafe-string toolchain, ran the complete regression suite, and generated the documentation successfully:

• Disposable control-statement CI run

The repository's ordinary matrix on the same source tree also passed both macOS jobs. Its Windows job compiled the changed OCaml modules before reaching an unchanged src/reg.c Win32 API type error, while its ordinary Linux job stopped during provisioning because the configured non-archived OCaml switch was unavailable:

• Ordinary matrix run

The disposable workflow was removed after validation and is not part of this pull request.