Use sensible first-float window sizing

[danwalmsley]

Summary

• treat tiny tracked dockable bounds as uninitialized during the first float operation
• fall back to the owner pane size before using the default 300x400 floating window size
• add a regression test covering first-float sizing when tracked document bounds are tiny

Testing

• dotnet build src/Dock.Model/Dock.Model.csproj -nologo
• dotnet test tests/Dock.Avalonia.HeadlessTests/Dock.Avalonia.HeadlessTests.csproj --filter FloatDockable_UsesOwnerSize_WhenTrackedDocumentBoundsAreTiny -nologo
• dotnet test tests/Dock.Avalonia.HeadlessTests/Dock.Avalonia.HeadlessTests.csproj -nologo

[wieslawsoltes]

@codex review

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid discarding persisted float sizes under 32px

The new ResolveFloatingSize threshold treats any tracked size <= 32 as uninitialized, so FloatDockable/FloatAllDockables now overwrite legitimate small persisted dimensions every time a dockable is floated again. In practice, if a user intentionally resizes a floating tool/document window to something narrow (for example 24px) and later docks then re-floats it, this code forces owner/default sizing instead of restoring the saved size, which is a regression from the previous NaN-only fallback behavior.

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[danwalmsley]

Addressed in 926f6bd0.

I narrowed the heuristic so we only treat clearly bogus initial tracked sizes as uninitialized by dropping the cutoff from 32 to 16. That preserves legitimate small persisted float sizes like 24x24 while still fixing the first-float tiny-window case.

I also added a regression test covering the preserved-small-size case:

• FloatDockable_PreservesSmallTrackedDocumentBoundsAboveTinyThreshold

And re-ran the focused sizing tests.