fix: adapter equality bug

[olliethedev]

Note

Medium Risk
Changes how findMany translates eq/ne comparisons against null, which can alter query results across supported databases if callers previously relied on =/<> behavior with nulls.

Overview
Fixes adapter filtering so where clauses using operator: "eq"/"ne" with value: null generate SQL IS NULL/IS NOT NULL instead of =/<> in both the Drizzle and Kysely adapters.

Adds end-to-end adapter tests covering null comparisons for single conditions and mixed AND/OR groups, and bumps @btst/* package versions from 2.1.0 to 2.1.1.

^{Written by Cursor Bugbot for commit d687b07. This will update automatically on new commits. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

^{Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}