[google_fonts] Remove failed loads from pendingFonts

[Yusufihsangorgel]

Failed font loads remain in pendingFontFutures because the current cleanup
callback runs only after successful completion. As a result, every later
GoogleFonts.pendingFonts() call rethrows the same completed error.

This change removes a tracked load on either completion path while preserving
the original error for the caller currently awaiting pendingFonts(). It adds
regression coverage showing that the first call reports the load failure and a
later call is no longer poisoned by it.

Fixes flutter/flutter#182430.

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[gemini-code-assist]

Code Review

This pull request updates the google_fonts package to version 8.2.1. It ensures that failed font loads are removed from pendingFontFutures by replacing then with whenComplete on the loading future in google_fonts_base.dart. A unit test has been added to verify that pendingFonts correctly removes failed font loads. There are no review comments, and I have no feedback to provide.

[mafreud]

@Yusufihsangorgel Is this PR going to fix this issue?
material-foundation/flutter-packages#534

[guidezpl]

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[Yusufihsangorgel]

Not directly. #534 is the load attempt itself failing (the fetch from fonts.gstatic.com throwing); after this PR that exception still happens once per failed load. What this PR fixes is one layer up: a failed load used to stay in pendingFontFutures, so every later GoogleFonts.pendingFonts() call rethrew the same completed error. If your Crashlytics noise is dominated by those repeats and the app uses pendingFonts(), this cuts it down to the single original failure; it does not prevent that first exception or add retrying.