chore: typecheck tests at build time
drop the per-package tsconfig.build.json files and let `tsgo` use the
default `tsconfig.json` (which already includes test and bench files).
this surfaces test/bench type errors at build time instead of letting
them rot silently. fixes the type errors that surfaced once the unified
build started seeing them: stale imports in the richtext-segmenter
bench, `number[]` buffers in the varint tests, internal-only car
helpers in the repo tests, and overbroad `unknown`/`Did` types in the
xrpc-server jwt-verifier tests.
publish artifacts are unchanged: every package now also excludes
`!dist/**/*.{test,bench}.*` via `package.json#files` so the compiled
test/bench output never ships.