refactor(rt): use frame ids in stack references

[Stevengre]

Summary

This draft refactors stack-based Reference/PtrLocal values to use stable frame ids instead of relative stack offsets.

What changed

• keep StackFrame frame ids as stable runtime identities
• make stack references and raw local pointers carry frame ids directly
• remove offset-adjustment helper layer and the corresponding lemmas
• resolve stack dereferences and writes by frame id
• update branch-specific expected outputs affected by the new representation

Validation

• make build
• uv --directory kmir run pytest src/tests/unit -q
• uv --directory kmir run pytest src/tests/integration/test_decode_value.py -q
• uv --directory kmir run pytest src/tests/integration/test_integration.py -q -x -k 'Ref-weirdRefs'
• uv --directory kmir run pytest src/tests/integration/test_integration.py -q -x -k 'main-a-b-c or closure-call'
• uv --directory kmir run pytest src/tests/integration/test_integration.py -q -x -k 'Ref-refAsArg or Ref-refReturned or Ref-doubleRef or iterator-simple'
• uv --directory kmir run pytest src/tests/integration/test_run_smir_random.py -q
• uv --directory kmir run pytest src/tests/integration/test_cli.py -q -k 'show_to_module or show_statistics_and_leaves or show_printers_snapshot'

Follow-up

PR #1003 can now be based on this draft and keep its pointer-cast/address-allocation work separate from the stack-reference-model refactor.

[Stevengre]

We don't need this because we can use size(stack) - OFFSET to get a stable identifier for frame.