Fixed an issue where EXPLAIN and EXPLAIN ANALYZE failed when blank lines separate clauses in the SQL query. (#9875)

getQueryAt now uses the syntax tree as the primary check for whether a
blank-line boundary cut through a SQL statement. It is split into two
helpers: _findQueryBoundaries (the original scan, parameterized by
stopAtBlankLine) and _needsExpansion, which detects when a Statement
node straddles the extracted range and re-scans ignoring blank lines.

A STATEMENT_STARTERS keyword list guards the case where the parser
merges semicolon-less queries into one Statement, and WRAPPER_STARTERS
(EXPLAIN, ANALYZE, WITH) force expansion when the Statement extends past
the range. Also fixes a Lezer boundary bug (tree.iterate is inclusive at
boundaries) with a node.to > startPos check. Adds 21 tests covering
EXPLAIN, negative no-merge cases, comments, and boundary edge cases.