BIP-119: Fix missing self. prefix on stack reference in pseudocode

## Summary In the `execute_bip_119` pseudocode, the hash comparison references `stack[-1]` instead of `self.stack[-1]`, inconsistent with all other stack references in the function: ```python # Correct: if len(self.stack) < 1: if len(self.stack[-1]) == 32: # Incorrect — missing self.: if stack[-1] != self.context.tx.get_default_check_template_hash(...) ``` In Python, `stack[-1]` would reference an undefined local variable, while `self.stack[-1]` correctly accesses the interpreter's stack. Th

Specification

# Correct:
if len(self.stack) < 1:
if len(self.stack[-1]) == 32:

# Incorrect — missing self.:
if stack[-1] != self.context.tx.get_default_check_template_hash(...)