[PR] refactor(sql): reduce copies of query context in PlannerContext (druid)

["FrankChen021 (via GitHub)" <gi...@apache.org>]

FrankChen021 opened a new pull request, #20630:
URL: https://github.com/apache/druid/pull/20630

   ### Description
   
   `PlannerContext` stored the query context as a mutable map, and every `queryContext()` call built a new `QueryContext` (a sorted copy) from it. `queryContext()` is called many times during planning.
   
   This PR makes `PlannerContext` hold a single immutable `QueryContext` and return it directly:
   
   - `queryContextMap()` now returns an immutable snapshot.
   - The four places that wrote into that map during planning (INSERT/REPLACE segment granularity, catalog `rowsPerSegment`, REPLACE time chunks, export file format) now use the new `PlannerContext#setQueryContextParameter`, which replaces the context with an overridden copy.
   - Added `QueryContext#override(QueryContextParameter<T>, T)`. It, and the existing `override(Map)`, now copy the context once instead of twice, and still keep keys sorted.
   - Removed the unused `PlannerContext#addAllToQueryContext`.
   
   <hr>
   
   This PR has:
   
   - [x] been self-reviewed.
   - [x] added unit tests or modified existing tests to cover new code paths.
   


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