test(tok): split integration_test.go into integration_advanced_test.go

Move the Performance, Configuration, concurrency, CompactionSchema, and
token-estimation-precision integration tests into a new same-package file
integration_advanced_test.go to keep integration_test.go under 1000 LOC.
Pure mechanical move; no test behavior changes.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: Patel230