fix(pytest_plugin): reject negative advance in _RecordingProgresser

[GreyViperTooth]

What

The emitter pytest fixture swaps the real progress bar for _RecordingProgresser, but that mock did not enforce a constraint the real _Progresser.advance does: it raises ValueError when amount < 0. As a result, tests using the fixture silently accepted negative advances that would crash in production, which can mask real bugs (this was noticed in canonical/craft-application#994).

How

• Give _RecordingProgresser.advance the same single-positional amount: float signature as the real _Progresser.advance.
• Add the same negative-amount guard (raise ValueError on amount < 0).
• The recorded-call format is unchanged (call(advance, 100)), so existing fixture assertions still hold.
• Add a regression test asserting the fixture now rejects a negative advance.

Fixes #466

🤖 Generated with Claude Code

[bepri]

Thanks! I left a little feedback below. Could you also add this as a bugfix in the changelog at docs/changelog.rst?

[bepri]

We can skip this addition to the docstring, I think.

[bepri]

This breaks the API of this fixture, I would do this instead:

Suggested change

	def advance(self, amount: float) -> None:
	def advance(self, *a: Any, amount: float, **k: Any) -> None:

(and update line 249 accordingly)

[GreyViperTooth]

Thanks @bepri! Kept the *a/**k passthrough and dropped the docstring as suggested. One tweak: I put amount first (def advance(self, amount, *a, **k)) instead of keyword-only, since *a, amount, **k would break the existing positional call progress_bar.advance(100). Also added the changelog entry.