Improve predicate-driven observation tracking in observer analyzer

[Copilot]

The observer analyzer wasn’t marking variables as observed when predicates (e.g., converged, stable) were used, leaving predicate checks without the required geometric tracking context.

• Observer logic

  • Track the last assigned identifier across assignments and tentative assignments.
  • Centralize predicate names via a class constant and reuse in predicate detection.
  • Ensure predicate conditions mark the last assigned variable as observed.

• Tests

  • Added targeted observer tests verifying predicate and not-predicate conditions mark the last assignment as observed.

Example:

observed = _analyze("""
    x is 1
    if converged:
        x is x + 1
""")
assert "x" in observed

Original prompt

Make improvements

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