Optimize trie builder

[gf2121]

This PR speeds up TrieBuilder and reduces its memory footprint by replacing the in-memory object tree with a compact prefix-coded byte buffer during the building phase, and using a frontier-based approach during the saving phase.

Previously, TrieBuilder constructed a large in-memory tree using Node objects. This approach was memory-intensive (O(total nodes * ~120 bytes per node)) and caused massive object allocations, which made it incredibly slow when dealing with large terms.

Main Changes

• Compact Byte Buffer (Building Phase): Replaced the object-heavy Node and SaveFrame classes with a sequential ByteBuffersDataOutput buffer. Entries are now prefix-encoded (storing prefix length, suffix length, and suffix bytes) and appended sequentially.
• Zero-Overhead Appends: The first non-empty key (minKey) is stored separately. This allows the append() method to re-encode only the first entry and bulk-copy the remaining bytes with zero per-entry overhead.
• Frontier-Based Save (Saving Phase): Reconstructs the trie structure on-the-fly during saveNodes() using a FrontierNode array bounded by maxKeyDepth, rather than requiring the whole tree to exist in memory.
• Removed Status Management: Remove status management because nothing got destroyed after append or save.
• No File Format Changes: The on-disk file format remains completely unchanged, ensuring backward compatibility.

Memory & Performance Impact

• Memory Usage: Drops from O(total nodes) to O(total encoded bytes) during building, and down to O(max key depth) during the save operation.
• Speed: Drastically reduces GC pressure and object allocations, bringing a massive speedup especially for very long terms.

[gf2121]

I get some number on building index of 1M uuids.

FINAL STATS (1 Million 16-byte UUIDs)

Metric	Old Trie	New Trie	FST	FST (No Suffix Sharing)
Memory Used (Before Saving)	673.06 MB	20.26 MB	57.57 MB	32.06 MB
Append Time	298.82 ms	166.27 ms	4587.17 ms	741.30 ms
Save Time	217.39 ms	218.97 ms	49.28 ms	46.27 ms
Total Time	516.21 ms	385.23 ms	4636.45 ms	787.57 ms