feat: support single-argument properties() for node, rel, and struct

[Mrhs121]

related to #831

[adsharma]

Nice feature overall. Two correctness concerns and a nit:

1. Null propagation: neither singleArgCompileFunc nor singleArgExecFunc writes the result's outer null mask. For an unflat input (the common case) exec hits the sel-vector equality check and skips entirely, so OPTIONAL MATCH (p:person {ID: 999}) RETURN properties(p) yields a non-null struct — and on the reference path its fields point at the null node's uninitialized child vectors (possibly stale data). openCypher says properties(null) is null. Please propagate outer nulls (or always do a sel-aligned copy) and add an OPTIONAL MATCH regression test.

2. Fragile invariant: correctness relies on resolveResultStateFromChildren assigning the child's state before compileFunc runs, so the state == check in compile matches the sel-pointer check in exec; if they ever disagree, the result is silently garbage rather than an error. Please document the contract, or unify both checks on parameters[0]->state.get() == result.state.get().

Nit: if (parameterSelVector == resultSelVector) continue; in singleArgExecFunc is loop-invariant — hoist it above the loop.

[adsharma]

Looks good. Requesting changes for the OPTIONAL MATCH and null handling. The other two comments are minor.

[Mrhs121]

Thanks for your review! I have addressed all the comments in the latest commit:

1. Null propagation: Added outer null mask propagation in singleArgExecFunc using setNullFromBits for unflat vectors and setNull for flat/filtered vectors, ensuring properties(null) evaluates to null. Added regression tests for OPTIONAL MATCH (null node / null relationship) and properties(null).
2. Contract & state check: Documented the zero-copy referencing contract in singleArgCompileFunc and unified the state check on parameters[0]->state.get() == result->state.get().
3. Loop-invariant hoisted: Hoisted the parameterSelVector == resultSelVector check out of the loop as an early return for the reference path.