feat(bindings): spanset follow-ups — lowercase aliases, hash, empty-array fix

[estebanzimanyi]

Summary

Three independent fixes for spanset, mirroring the corresponding set-level work in PRs #8, #10, and #11:

1. Lowercase splitNspans / splitEachNspans aliases

Adds the lowercase forms for all five spanset types (intspanset/bigintspanset/floatspanset/datespanset/tstzspanset) pointing at the same Spanset_split_n_spans / Spanset_split_each_n_spans dispatchers as the existing camelCase registrations. The camelCase forms stay registered for back-compat.

2. spanset_hash / spanset_hash_extended

• spanset_hash(<spanset>) -> UINTEGER (MEOS uint32 spanset_hash)
• spanset_hash_extended(<spanset>, BIGINT seed) -> UBIGINT (MEOS uint64 spanset_hash_extended; seed cast to uint64)

Implementation mirrors set_hash / span_hash: copies the blob into a malloc'd SpanSet, calls MEOS, frees. Registered in the per-spanset-type loop in src/temporal/spanset.cpp.

3. Empty-array spanset() constructor

Spanset_constructor in src/temporal/spanset_functions.cpp built a Span array from a DuckDB list and called the MEOS constructor without checking length. On an empty input list MEOS returned NULL, surfacing later as Invalid Input Error: Null pointer not allowed. Adds a length == 0 check that raises InvalidInputException("The input array cannot be empty"), matching the message MEOS itself uses.

Smoke test

SELECT splitNspans(intspanset '{[1,2),[3,4),[5,6)}', 2);          -- ['[1, 4)', '[5, 6)']
SELECT spanset_hash(intspanset '{[1,2]}');                         -- 2065175519 (UINTEGER)
SELECT spanset_hash_extended(tstzspanset '{[2000-01-01,2000-01-02]}', 1);
                                                                   -- 13017976434127639608 (UBIGINT)
SELECT spanset(ARRAY[]::TSTZSPAN[]);
  -- Invalid Input Error: The input array cannot be empty

Test plan

• make release then TZ=UTC ./build/release/test/unittest "<proj>/test/*" — full suite passes.

Activates the corresponding skip blocks in test/sql/parity/007_spanset.test (open in PR #18) once both land.