fix(python): make sure explain_plan works with FTS queries (#2466)

## Summary

Fixes issue #2465 where FTS explain plans only showed basic `LanceScan`
instead of detailed execution plans with FTS query details, limits, and
offsets.

## Root Cause

The `FTSQuery::explain_plan()` and `analyze_plan()` methods were missing
the `.full_text_search()` call before calling explain/analyze plan,
causing them to operate on the base query without FTS context.

## Changes

- **Fixed** `explain_plan()` and `analyze_plan()` in `src/query.rs` to
call `.full_text_search()`
- **Added comprehensive test coverage** for FTS explain plans with
limits, offsets, and filters
- **Updated existing tests** to expect correct behavior instead of buggy
behavior

## Before/After

**Before (broken):**
```
LanceScan: uri=..., projection=[...], row_id=false, row_addr=false, ordered=true
```

**After (fixed):**
```
ProjectionExec: expr=[id@2 as id, text@3 as text, _score@1 as _score]
  Take: columns="_rowid, _score, (id), (text)"
    CoalesceBatchesExec: target_batch_size=1024
      GlobalLimitExec: skip=2, fetch=4
        MatchQuery: query=test
```

## Test Plan

- [x] All new FTS explain plan tests pass 
- [x] Existing tests continue to pass
- [x] FTS queries now show proper execution plans with MatchQuery,
limits, filters

Closes #2465

🤖 Generated with [Claude Code](https://claude.ai/code)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Tests**
* Added new test cases to verify explain plan output for full-text
search, vector queries with pagination, and queries with filters.

* **Bug Fixes**
* Improved the accuracy of explain plan and analysis output for
full-text search queries, ensuring the correct query details are
reflected.

* **Refactor**
* Enhanced the formatting and hierarchical structure of execution plans
for hybrid queries, providing clearer and more detailed plan
representations.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Claude <noreply@anthropic.com>

python/src/query.rs

@@ -563,7 +563,10 @@ impl FTSQuery {
     }
 
     pub fn explain_plan(self_: PyRef<'_, Self>, verbose: bool) -> PyResult<Bound<'_, PyAny>> {
-        let inner = self_.inner.clone();
+        let inner = self_
+            .inner
+            .clone()
+            .full_text_search(self_.fts_query.clone());
         future_into_py(self_.py(), async move {
             inner
                 .explain_plan(verbose)
@@ -573,7 +576,10 @@ impl FTSQuery {
     }
 
     pub fn analyze_plan(self_: PyRef<'_, Self>) -> PyResult<Bound<'_, PyAny>> {
-        let inner = self_.inner.clone();
+        let inner = self_
+            .inner
+            .clone()
+            .full_text_search(self_.fts_query.clone());
         future_into_py(self_.py(), async move {
             inner
                 .analyze_plan()