feat(query): add use_lsm to read MemWAL LSM data (#3489)

## What

MemWAL LSM **read** support. When a table has an LSM write spec
(`set_lsm_write_spec`), `merge_insert` upserts live in the MemWAL
active/frozen memtables and flushed SSTables until an external
compaction merges them into the base table, so a normal scan returns
**stale** data. This routes reads through Lance's `LsmScanner` so
queries also surface that in-flight data, deduplicated by primary key
(newest generation wins).

## How

- Adds a **`use_lsm: Option<bool>`** query flag, symmetric with the
`merge_insert` flag:
- **unset** — auto-route through the LSM scanner when the table carries
a write spec
- **`use_lsm(true)`** — force the LSM path; error if there is no spec
    - **`use_lsm(false)`** — read the base table only (the escape hatch)
- Plain scan, single-column full-text search, and single-vector ANN all
run through one `LsmScanner` (assembled from on-disk shard manifests
plus the cached writer's in-memory memtables), so a `where` predicate is
honored as a **prefilter** uniformly — including for vector search.
- **Compaction-aware snapshots:** an SSTable generation is dropped only
once it is both compacted into the base table and covered by the arm's
base-index catch-up (`index_catchup`); plain scans use the compaction
watermark alone.
- Query shapes the scanner cannot honor hard-error with guidance to set
`use_lsm(false)`: hybrid, multi/binary vectors, `with_row_id`,
reranking, `order_by`, dynamic/Substrait projection or filters,
`distance_range`, `use_index(false)`, postfilter, take-by-row-id/offset,
reads from a time-traveled version, and an unmaintained or ambiguous
(multiple) FTS/vector index. Namespace-pushdown queries fall back to
local execution when a spec is present; WAL-only writers are handled.
- Exposed across the Rust core and the Python (`use_lsm`) and TypeScript
(`useLsm`) bindings, including `TakeQuery`.

Rebased from Lance `7.2.0-beta.3` to `10.0.0-beta.3`.

python/src/table.rs

@@ -1215,8 +1215,8 @@ impl Table {
         if let Some(use_index) = parameters.use_index {
             builder.use_index(use_index);
         }
-        if let Some(use_lsm_write) = parameters.use_lsm_write {
-            builder.use_lsm_write(use_lsm_write);
+        if let Some(use_lsm) = parameters.use_lsm {
+            builder.use_lsm(use_lsm);
         }
         if let Some(validate_single_shard) = parameters.validate_single_shard {
             builder.validate_single_shard(validate_single_shard);
@@ -1454,7 +1454,7 @@ pub struct MergeInsertParams {
     when_not_matched_by_source_condition_expr: Option<PyExpr>,
     timeout: Option<std::time::Duration>,
     use_index: Option<bool>,
-    use_lsm_write: Option<bool>,
+    use_lsm: Option<bool>,
     validate_single_shard: Option<bool>,
 }