refactor(pvirtq): combine u15 offset and u1 wrap counter in more places

[mkroening]

This PR makes use of the offset + wrap bitfield for saving one byte per index. I am not sure if there is any performance change, but this also makes the code more readable by combining these related fields.

Depends on #2046.

[github-actions]

Benchmark Results

Benchmark	Current: ea294d7	Previous: b966ab4	Performance Ratio
startup_benchmark Build Time	115.06 s	111.96 s	1.03
startup_benchmark File Size	0.91 MB	0.91 MB	1.00
Startup Time - 1 core	0.94 s (±0.03 s)	0.93 s (±0.02 s)	1.00
Startup Time - 2 cores	0.92 s (±0.03 s)	0.93 s (±0.03 s)	0.98
Startup Time - 4 cores	0.92 s (±0.03 s)	0.93 s (±0.03 s)	0.99
multithreaded_benchmark Build Time	114.86 s	114.77 s	1.00
multithreaded_benchmark File Size	1.02 MB	1.01 MB	1.00
Multithreaded Pi Efficiency - 2 Threads	89.00 % (±7.16 %)	88.97 % (±7.38 %)	1.00
Multithreaded Pi Efficiency - 4 Threads	43.56 % (±3.34 %)	44.09 % (±3.63 %)	0.99
Multithreaded Pi Efficiency - 8 Threads	25.73 % (±2.14 %)	25.36 % (±1.99 %)	1.01
micro_benchmarks Build Time	296.36 s	295.64 s	1.00
micro_benchmarks File Size	1.02 MB	1.02 MB	1.00
Scheduling time - 1 thread	174.22 ticks (±22.97 ticks)	178.23 ticks (±25.33 ticks)	0.98
Scheduling time - 2 threads	107.05 ticks (±18.69 ticks)	98.66 ticks (±14.00 ticks)	1.09
Micro - Time for syscall (getpid)	12.02 ticks (±10.15 ticks)	11.98 ticks (±4.92 ticks)	1.00
Memcpy speed - (built_in) block size 4096	61488.74 MByte/s (±43301.44 MByte/s)	63152.99 MByte/s (±45587.10 MByte/s)	0.97
Memcpy speed - (built_in) block size 1048576	14260.67 MByte/s (±11591.85 MByte/s)	15668.33 MByte/s (±12904.18 MByte/s)	0.91
Memcpy speed - (built_in) block size 16777216	9873.42 MByte/s (±7962.15 MByte/s)	10465.02 MByte/s (±8568.62 MByte/s)	0.94
Memset speed - (built_in) block size 4096	61869.80 MByte/s (±43575.40 MByte/s)	63370.25 MByte/s (±45752.42 MByte/s)	0.98
Memset speed - (built_in) block size 1048576	14559.60 MByte/s (±11773.86 MByte/s)	15907.38 MByte/s (±12989.07 MByte/s)	0.92
Memset speed - (built_in) block size 16777216	10124.27 MByte/s (±8112.18 MByte/s)	10679.75 MByte/s (±8675.34 MByte/s)	0.95
Memcpy speed - (rust) block size 4096	53703.78 MByte/s (±40172.73 MByte/s)	56435.01 MByte/s (±41692.91 MByte/s)	0.95
Memcpy speed - (rust) block size 1048576	13436.59 MByte/s (±11026.86 MByte/s)	14141.32 MByte/s (±11788.91 MByte/s)	0.95
Memcpy speed - (rust) block size 16777216	9647.20 MByte/s (±7759.02 MByte/s)	10587.80 MByte/s (±8680.27 MByte/s)	0.91
Memset speed - (rust) block size 4096	54256.70 MByte/s (±40611.12 MByte/s)	57311.29 MByte/s (±42263.04 MByte/s)	0.95
Memset speed - (rust) block size 1048576	13780.27 MByte/s (±11229.11 MByte/s)	14556.89 MByte/s (±12036.69 MByte/s)	0.95
Memset speed - (rust) block size 16777216	9879.64 MByte/s (±7892.83 MByte/s)	10801.86 MByte/s (±8787.27 MByte/s)	0.91
alloc_benchmarks Build Time	292.53 s	295.50 s	0.99
alloc_benchmarks File Size	0.98 MB	0.98 MB	1.00
Allocations - Allocation success	100.00 %	100.00 %	1
Allocations - Deallocation success	100.00 %	100.00 %	1
Allocations - Pre-fail Allocations	100.00 %	100.00 %	1
Allocations - Average Allocation time	22711.26 Ticks (±1136.06 Ticks)	22283.43 Ticks (±1951.06 Ticks)	1.02
Allocations - Average Allocation time (no fail)	22711.26 Ticks (±1136.06 Ticks)	22283.43 Ticks (±1951.06 Ticks)	1.02
Allocations - Average Deallocation time	2704.44 Ticks (±1094.24 Ticks)	2877.16 Ticks (±1320.24 Ticks)	0.94
mutex_benchmark Build Time	292.65 s	295.15 s	0.99
mutex_benchmark File Size	1.02 MB	1.02 MB	1.00
Mutex Stress Test Average Time per Iteration - 1 Threads	37.50 ns (±3.83 ns)	37.34 ns (±4.31 ns)	1.00
Mutex Stress Test Average Time per Iteration - 2 Threads	31.22 ns (±3.11 ns)	30.54 ns (±3.08 ns)	1.02

This comment was automatically generated by workflow using github-action-benchmark.

[Gelbpunkt]

Not sure about perf here since bitfields should have generally worse access times due to the necessary bitshifts as opposed to doing them once and using an intermediate struct for holding the values. I don't really mind either way, but this version feels like we're at least not reinventing virtio-spec

[mkroening]

Makes sense. I renamed the commits to imply only a refactor. Merging this once CI passes.