[AjayBrahmakshatriya]

Summary

Fixes #119.

Loop backedges usually target a label in the current statement block or
one of its parent scopes. However, first-stage compiler optimizations
such as tail merging or loop rotation can place the label and backedge
in sibling scopes.

The existing loop finder cannot recognize this structure and may remove
the label while leaving its goto behind, producing invalid generated
code.

This PR adds a normalization pass before loop discovery. For each
sibling-scope backedge, the pass:

• Finds the common parent of the target label and its backedges.
• Copies the continuation following the label to each out-of-scope goto.
• Redirects the copied continuation through a new label in the common
  parent, restoring the structure expected by the loop finder.
• Handles nested scopes recursively and stops copying at a goto or
  return.
• Hoists declarations from copied continuations while leaving their
  initializations on the original and copied execution paths.
• Leaves labels intact when they still have non-local references that
  cannot be normalized.

Declaration splitting helpers previously local to the for-loop finder
are moved into a shared utility for use by the normalization logic.

Tests

Added sample67 covering:

• A merged first iteration with the same loop body.
• A merged first iteration with a different prefix.
• A normalized loop followed by another loop.

Golden outputs are included for both normal variable extraction and
variable-name recovery.

Validated with:

• make TEST=sample67 run
• make BUILD_DIR=/tmp/buildit-varnames RECOVER_VAR_NAMES=1 TEST=sample67 run