Fix moment commutation detection for group-commuting operations (#6659)

[chamodtharakaperera]

Fixes #6659

This PR fixes an issue where cirq.commutes() incorrectly returns False for moments that commute as a whole even when their individual operations don't commute. For example, given two Z gates and an RXX gate, [Z⊗Z, RXX] = 0 even though neither Z commutes with RXX individually.

The solution:

• First tries fast path of checking individual operation commutation
• If individual operations don't commute or result is indeterminate, falls back to checking if the full moments commute via unitary calculation
• Properly handles edge cases:
  • Disjoint qubit sets (trivially commute)
  • Non-unitary operations (returns NotImplemented)
  • Indeterminate cases (returns NotImplemented)

Added comprehensive test cases covering:

• Original Z⊗Z with RXX commutation case
• Disjoint qubit operations
• Mixed cases where some operations commute individually and others as a group
• Non-commuting cases to verify negative results
• Complex cases requiring unitary calculation

Test outputs demonstrate correct behavior for all cases including the original issue where Z⊗Z should commute with RXX.

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