Batch INSERT statements in executemany to reduce round trips

[srchilukoori]

Description

Fixes #602.

Cursor.executemany() executes INSERT...VALUES one row at a time.
For 1,000 rows that means 1,000 HTTP round trips to Trino.

This adds a regex check for INSERT...VALUES patterns and batches
rows into multi-row VALUES clauses, 100 per request. Non-INSERT
statements still use the existing row-by-row path. Parameters are
formatted with the existing _format_prepared_param() method.

Scenario	Row-by-row	Batched	Speedup
500 rows x 2 cols	8.9s	0.23s	~39x
1,000 rows x 25 cols (mixed types)	timeout	3.1s (322 rows/s)	—

Non-technical explanation

Bulk inserts via SQLAlchemy text() or cursor.executemany() now
send fewer queries to Trino instead of one per row.

Release notes

( ) This is not user-visible or docs only and no release notes are required.
( ) Release notes are required, please propose a release note for me.
(x) Release notes are required, with the following suggested text:

* Batch INSERT...VALUES in `executemany()` into multi-row statements to reduce HTTP round trips. ({issue}`602`)

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