Resume compilation of the clients generated by tests

[requiel20]

progenitor-impl/tests/output exists so the checked-in output of the generator is
compiled, not only compared as text. Nothing compiles it. The crate declares its own
[workspace], so a build from the repo root never reaches it, no CI job names the
directory, and its Cargo.lock is gitignored, so no lock file recorded any drift.

It has not built for a while. cargo build in that directory reports 1855 errors on
current main.

Most of them are because five of its dependencies fell behind the ones the workspace
resolves, and since progenitor-client is a path dependency asking for reqwest 0.13
while this crate asked for 0.12, two versions of reqwest met in one tree. This PR
bumps all those dependencies:

	was	now
base64	0.21	0.23
httpmock	0.7	0.8
rand	0.8	0.10
regress	0.7	0.12
reqwest	0.12	0.13

Another error comes from the generated buildomat CLI asking clap for a value parser
it cannot infer. The crate now supplies it through ValueParserFactory.

Finally, the crate must use rust 2021 as it emits the gen word in the code, which is
reserved in Rust 2024.

Two changes keep it from regressing again:

• build the crate in CI
• have dependabot watch the crate