Implement `request.expectParams()` to coerce params to a given struct.
`request.paramsInfo()` provides information about each param (present,
blank, failed + original values and errors where applicable).
Add `jetzig test` command which runs build step `jetzig:test`.
Add `jetzig.testing` namespace which provides test helpers and a test
app.
Add tests to view generator (i.e. include tests for generated routes).
Use in-memory KV store (JetKV) for simple job queue.
Build script generates an array of Zig modules in `src/app/jobs/` and
stores their name + run function (`run(allocator, params, logger)`).
View functions schedule jobs with arbitrary params.
Thread pool spawns a (configurable) number of workers and pops jobs from
the queue, then invokes the appropriate run function.
