test: use TypeScript Go

[metonym]

Use TypeScript Go for typechecking.

Before

hyperfine --warmup 3 --runs 5 'bun test:src-types'
Benchmark 1: bun test:src-types
  Time (mean ± σ):      1.099 s ±  0.020 s    [User: 2.773 s, System: 0.110 s]
  Range (min … max):    1.068 s …  1.121 s    5 runs

After

Benchmark 1: bun test:src-types
  Time (mean ± σ):     142.2 ms ±   2.1 ms    [User: 537.5 ms, System: 92.6 ms]
  Range (min … max):   140.1 ms … 145.6 ms    5 runs