[tisonkun]

XOR membership queries need the construction seed, segment layout, and fingerprints, but not the number of input hashes. Remove the finished filter's count and getNumItems(), isEmpty(), and getBitsPerItem(). The builder still tracks its updates.

The serialized header occupies 24 bytes: flags at byte 3, fingerprint width at byte 4, seed at byte 8, and segment length at byte 16. Remaining bytes are reserved. Writers emit zero flags; readers reject unsupported flags. The layout has three fingerprint segments and no persisted item count.

Release compatibility needs resolution before merging. Java 9.1.0-RC1 contains the count-bearing version-1 format and the three public methods. This PR currently retains serialization version 1 and removes those methods. If that release ships first, this PR needs a distinct format version with a legacy reader, and an agreed API migration. It must not be released as a compatible minor update in its current form.

Validation: mvn -B clean verify passes all 2,335 tests. Coverage includes heapify/wrap round trips, reference images, unsupported flags, truncated images, fingerprint widths, hash count, and capacity invariants. The preamble error message now refers to longs rather than bytes.

[tisonkun]

The Rust counterpart uses the same header and serialization version 1. Its serialization tests consume scalar and UTF-8/raw-byte fixtures generated from this PR's c179c5bc0 and verify byte-for-byte construction and round trips.