fix: parser treats 'atomic' in identifiers as BEGIN ATOMIC keyword

[7ttp]

Summary

Parser incorrectly treats atomic substring in identifiers as BEGIN ATOMIC keyword, causing migration failures.

Problem

Migrations with table/column names containing atomic fail with:
ERROR: cannot insert multiple commands into a prepared statement (SQLSTATE 42601)

Example:

create table public.atomic_test (id int);
select 1;

Root cause: Parser matches atomic in identifiers as the BEGIN ATOMIC keyword, enters a state where semicolons are ignored, and merges multiple statements into one.

Solution

Added word boundary check: ATOMIC only recognized as keyword when preceded by whitespace.
This prevents false matches in identifiers while preserving correct BEGIN ATOMIC function body handling.

Related

• Closes Database migration fails on local server when table or column name contains 'atomic' #4746