refactor(virtio): bundle worker parameters into WorkerParam

[Lencerf]

Virtio::spawn_worker(), Mio::spawn_worker(), IoUring::spawn_worker() and Worker::spawn() all took the same three arguments: the wake event receiver, the guest memory bus and the queue registers. Every device implementation merely forwarded them, and each new field had to be threaded through every signature and call site.

Introduce WorkerParam, built once by VirtioDevice::new() and passed down as a whole. Context embeds it instead of copying its fields, so adding a shared field only touches WorkerParam and VirtioDevice::new(). Device implementations never look inside.

No functional change.

Assisted-by: Antigravity:Claude-Fable-5.1

[coveralls]

Coverage Report for CI Build 37284591117

Coverage increased (+0.05%) to 39.088%

Details

• Coverage increased (+0.05%) from the base build.
• Patch coverage: 24 uncovered changes across 9 files (14 of 38 lines covered, 36.84%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
alioth/src/virtio/dev/dev.rs	12	6	50.0%
alioth/src/virtio/dev/blk.rs	3	0	0.0%
alioth/src/virtio/dev/net/tap.rs	3	0	0.0%
alioth/src/virtio/dev/balloon.rs	2	0	0.0%
alioth/src/virtio/dev/fs/fs.rs	2	0	0.0%
alioth/src/virtio/dev/fs/vu.rs	2	0	0.0%
alioth/src/virtio/dev/net/vmnet.rs	2	0	0.0%
alioth/src/virtio/dev/vsock/vhost_vsock.rs	2	0	0.0%
alioth/src/virtio/vu/frontend.rs	2	0	0.0%
Total (13 files)	38	14	36.84%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	15509
Covered Lines:	5890
Line Coverage:	37.98%
Relevant Branches:	1642
Covered Branches:	814
Branch Coverage:	49.57%
Branches in Coverage %:	Yes
Coverage Strength:	922.12 hits per line

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💛 - Coveralls