fix: model-based tests intermittently timeout (5s limit)

[BYK]

Problem

Several model-based tests using fast-check intermittently timeout with the default 5000ms limit:

• test/lib/db/model-based.test.ts — "alias lookup is case-insensitive"
• test/lib/db/pagination.model-based.test.ts — "get on empty table returns undefined", "composite key: different command keys are independent"
• test/lib/db/dsn-cache.model-based.test.ts — "random sequences of cache operations maintain consistency"

These fail even when run in isolation:

bun test test/lib/db/model-based.test.ts test/lib/db/pagination.model-based.test.ts test/lib/db/dsn-cache.model-based.test.ts
# 13 pass, 5 fail — all timeouts

Possible fixes

1. Increase the per-test timeout for model-based tests (e.g., test.timeout(15_000))
2. Reduce DEFAULT_NUM_RUNS or number of commands generated per run
3. Profile to find which command sequences are slow (likely DB-heavy sequences with many upserts)

Impact

Low — these are property-based tests that occasionally hit slow command sequences. CI usually passes because the timeouts are intermittent.