fix(cuda): retain pinned sources across transfer failures

Validate the transfer context and wait for the previous source fence before replacing it. On submission or fence failure, synchronize the stream before recycling the source, retaining the allocation if completion cannot be established. Include ownership regression tests and bind the context explicitly before pinned allocation.

Original-commit: 94897853df
Original-commit: a2f6ce3b37
Signed-off-by: Alexander Droste <alexander.droste@protonmail.com>

Author: 0ax1