bindings/python: +fix Make Transition hashable and drop misspelled __neq__

[Adda0]

Transition defined eq without hash, which under Cython 3 (like in Python) sets
hash to None, so transitions raised TypeError: unhashable type when put into a set or
used as a dictionary key. Transition exposes no setters, so its instances are immutable and
can be hashed safely: hash now returns hash((source, symbol, target)), consistent with
eq. The neq methods on Transition and SymbolPost were dead code -- Python calls
ne, and != already follows from eq -- and are removed, along with their entries in
the .pyi stub. SymbolPost deliberately stays unhashable: its symbol and targets setters make
instances mutable.

New test test_transition_hashing in bindings/python/tests/test_nfa.py checks equal hashes,
set deduplication (len({first, second, other}) == 2), dict keying and !=. It fails with
TypeError before the fix. just bindings::python::test: 132 passed, 3 skipped, 2 xfailed.

Fixes #853.

Fixes #853

[greptile-apps]

Confidence Score: 5/5

[Medium risk] Fixes Python bindings for transition object behavior.

The PR appears safe to merge; no actionable issues were found.

What we checked:

• Transition keys stay stable: Python cannot set the three fields. Returned transitions own separate copies, so changing an automaton does not change an existing key.

Summary

Makes Transition usable in sets and as dictionary keys by hashing its three fields.

• Removes unused __neq__ methods and updates the type declarations.
• Adds tests for equal hashes, set deduplication, dictionary keys, and inequality.
• No actionable issues found. Tests were not run during this review.

_{Reviews (1) · Last reviewed commit: "bindings/python: +fix Make Transition ha..." · Reviewed by Greptile}