style: use lowercase subtest names in test files

## Summary

Several test files use capitalized subtest names:

```go
t.Run("Test GetByID", func(t *testing.T) { ... })
t.Run("Test FilterWithColumn", func(t *testing.T) { ... })
```

Go convention for `t.Run()` names is fully lowercase descriptive phrases:

```go
t.Run("get by id", func(t *testing.T) { ... })
t.Run("filter with column", func(t *testing.T) { ... })
```

This reads more naturally in test output and follows the convention used in the standard library and most Go projects.

## Affected Files

- `examples/typed/query_test.go` — 6 subtests
- `examples/typed/filters/blacklist/iface_test.go`
- `examples/typed/filters/whitelist/iface_test.go`
- `examples/typed/filters/twolevel/iface_test.go`
- `examples/typed/filters/twolevel/nested/iface_test.go`
- `examples/typed/filters/pattern/iface_test.go`

## References

- [Go Code Review Comments — Use of subtests](https://github.com/golang/go/wiki/CodeReviewComments#use-of-subtests)