Fixes#2190
The `q` value with chunk transmissions is a bit complicated. The initial
transmission ("start" command) `q` value is used for all subsequent
chunks UNLESS a subsequent chunk specifies a `q >= 1`. If a chunk
specifies `q >= 1`, then that `q` value is subsequently used for all
future chunks unless another chunk specifies `q >= 1`. And so on.
This commit importantly also introduces the ability to test a full Kitty
command from string request to structured response. This will let us
prevent regressions in the future and ensure that we are correctly
handling the complex underspecified behavior of Kitty Graphics.
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