test: consolidate regex/patterns/findMatches tests into index.test.ts

[otnc]

The three test files had grown overlapping/redundant coverage: most of regex.test.ts's individual case list (single-pattern checks like "うおw") duplicated what the per-pattern loop in patterns.test.ts already verifies more precisely (tied to the pattern's own id). Consolidated into one test/index.test.ts:

• findAll/contains: kept only the scenarios not covered elsewhere (basic smoke check, the (笑)-with-stem regression, multi-pattern findAll matching, and argument validation - the last of these wasn't tested anywhere before)
• findMatches: unchanged, moved as-is
• パターン別サンプル: the auto-generated per-pattern loop, now also asserting findMatches returns the same pattern id for each sample (so both the combined-regex path and the per-pattern-regex path are exercised)

Net effect: 3 files / ~120 tests with real duplication -> 1 file / 140 tests with each one covering something the others don't.