Reuse hash_list_primitive! for string/binary list elements and factor out map-entry hashing loops #6984

What is the problem the feature request solves?

native/spark-expr/src/hash_funcs/utils.rs hand-expands the same null-aware hashing loop in several places:

• Inside hash_list_with_primitive_elements!, the Utf8 and Binary arms repeat the null/no-null double loop that hash_list_primitive! already provides, once for the offsets variant (L334-L388, L389-L426) and once for the fixed-size variant (L433-L485, L486-L521).
• The Map arm (L1110-L1219) repeats a null-aware loop four times, for (Utf8, Int32), (Int32, Utf8), (Utf8, Utf8) and (Int32, Int32), differing only in the downcast type and .to_le_bytes() on the integer side.

The copies are consistent today, but any change to null handling in hashing has to be made in eight or more places, and hash results must match Spark exactly.

Describe the potential solution

• Call hash_list_primitive! for Utf8 and Binary elements (with an identity transform) in both the offsets and fixed-size variants, and delete the hand-written loops.
• For the Map arm, add a hash_map_entries! helper macro, or a generic function taking key/value accessor closures that produce impl AsRef<[u8]>, and instantiate it for the four type pairs.
• Verify with the existing murmur3/xxhash64 tests and a benchmark that inlining is preserved.

Additional context

This is self-contained and a good first issue. Line references are pinned to commit 7d8d9b1.