Preserve Bitmap-Only IDs In Numeric Buckets

[shaleenji]

Description

Numeric buckets can contain IDs only in summary_bitmap after saturated duplicate inserts. Some paths still treat ids as the source of truth, so bitmap-only IDs can be skipped, dropped, or cause a bucket to be deleted incorrectly.

Steps to Reproduce

1. Insert more than Bucket::MAX_SIZE documents with the same numeric value.
2. Remove IDs or insert another value that triggers bucket split behavior.
3. Query the exact numeric value and compare results with inserted live IDs.

Expected Behavior

All live IDs should remain queryable and removable whether represented in ids/deltas or only in summary_bitmap.

Actual Behavior

Bucket::is_empty(), range handling for empty ids, and split bitmap rebuilds can ignore or drop bitmap-only IDs.