gh-148278: Fix try except block bug

[Shubham-Developer02]

Summary

• Fix missing/incorrect exception table coverage for some try regions by labeling block-setup and block-pop pseudos with the active handler in label_exception_targets().
• Add regression tests that assert relevant bytecode offsets fall inside a try entry in co_exceptiontable.

Fixes #148278.

Details

label_exception_targets() assigns instr->i_except, which becomes co_exceptiontable ranges after assembly. Previously:

• SETUP_FINALLY (and other is_block_push instructions) updated the internal except stack but did not set instr->i_except, so the start of the protected span could be absent from the table.
• POP_BLOCK was rewritten to NOP without setting instr->i_except, which could split or omit coverage for the following instruction (notably continue’s backward jump, or minimal try bodies).

The fix sets instr->i_except appropriately for those instructions so tracing and pending exceptions on those offsets resolve to the intended except handler.

Tests

• Lib/test/test_compile.py (TestSpecifics):
  • test_while_continue_try_except_exception_table
  • test_try_literal_stmt_exception_table

• Issue: Exceptions raised while tracing certain statements cannot be caught #148278

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