[WIP] Add Xor Filter to the filters package

[freakyzoidberg]

Summary

Adds an immutable Xor Filter for probabilistic set membership to a new org.apache.datasketches.filters.xorfilter package, as a smaller/faster alternative to the existing Bloom filter. The API, naming, Javadoc, exception handling, serialization layout, and MemorySegment support mirror BloomFilter.

Implements the algorithm from Graf & Lemire, "Xor Filters: Faster and Smaller Than Bloom and Cuckoo Filters," ACM JEA 2020, with 8-bit and 16-bit fingerprints.

What's included

• XorFilter — immutable filter: peeling construction, 3-hash membership query, the full typed query(...) suite (long/double/String/byte[]/char[]/ short[]/int[]/long[]/MemorySegment), heapify/wrap, toByteArray/toLongArray, and a BloomFilter-style toString.
• XorFilterBuilder — accumulates items via a matching typed update(...) suite, de-duplicates, and builds; plus static create(long[]...) factories.
• package-info.java, XorFilterTest (24 tests), and a standalone XorFilterBenchmark.
• Family: new XORFILTER(22, "XORFILTER", 3, 3) entry.

Design notes

• Items are reduced to 64-bit keys once (xxHash64), then mapped to positions and a fingerprint via a MurmurHash3 finalizer keyed on a construction seed that is re-drawn (splitmix64) if a rare 2-core remains, capped at 100 attempts.
• Fingerprint array capacity is floor(1.23*n) + 32, rounded down to a multiple of 3.
• Serialization uses a fixed 3-long preamble (the filter has no empty/growable state) followed by the raw fingerprint bytes; layout is documented in an ASCII table in XorFilter.

Testing

• 24 new unit tests + existing filters/Family tests pass on JDK 25 (no false negatives; typed items; duplicates; empty; determinism; heapify/wrap/toLongArray round-trips for 8- and 16-bit; corruption guards).
• apache-rat license check passes (0 unapproved).
• Benchmark confirms the paper's expectations: bits/item = 9.84 (8-bit) / 19.68 (16-bit); observed FPP ~= 1/256 and ~= 1/65536.

Follow-ups (not in this PR)

• Cross-language (C++/Go) serialization compatibility test, a la BloomFilterCrossLanguageTest.