✨ Simplify and speedup priority queue

[inteon]

I reviewed the priority queue source code, simplified it and tried to improve the benchmarks.

$ go test -run=^$ -benchmem -bench ^Benchmark sigs.k8s.io/controller-runtime/pkg/controller/priorityqueue -count 10 > main.out
$ go test -run=^$ -benchmem -bench ^Benchmark sigs.k8s.io/controller-runtime/pkg/controller/priorityqueue -count 10 > pr.out
$ benchstat main.out pr.out 
goos: linux
goarch: amd64
pkg: sigs.k8s.io/controller-runtime/pkg/controller/priorityqueue
cpu: Intel(R) Core(TM) Ultra 7 165H
                   │   main.out    │                pr.out                │
                   │    sec/op     │    sec/op     vs base                │
AddGetDone-8         1048.9µ ±  2%   300.1µ ±  2%  -71.39% (p=0.000 n=10)
AddOnly-8             91.11µ ± 22%   26.98µ ±  4%  -70.39% (p=0.000 n=10)
AddLockContended-8   121.87µ ± 28%   45.08µ ± 22%  -63.01% (p=0.000 n=10)
geomean               226.7µ         71.46µ        -68.47%

                   │     main.out     │                 pr.out                 │
                   │       B/op       │     B/op       vs base                 │
AddGetDone-8           273.64Ki ±  0%   31.30Ki ±  0%   -88.56% (p=0.000 n=10)
AddOnly-8            193930.000 ± 15%     2.000 ±  0%  -100.00% (p=0.000 n=10)
AddLockContended-8    221.532Ki ± 17%   3.563Ki ± 29%   -98.39% (p=0.000 n=10)
geomean                 225.6Ki           616.1         -99.73%

                   │   main.out    │                  pr.out                   │
                   │   allocs/op   │  allocs/op    vs base                     │
AddGetDone-8           5.014k ± 0%   1.000k ±  0%   -80.06% (p=0.000 n=10)
AddOnly-8              1.000k ± 0%   0.000k ±  0%  -100.00% (p=0.000 n=10)
AddLockContended-8   1071.000 ± 2%    2.000 ± 50%   -99.81% (p=0.000 n=10)
geomean                1.751k                      ?                       ¹ ²
¹ summaries must be >0 to compute geomean
² ratios must be >0 to compute geomean

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[alvaroaleman]

This change is doing way too many many things at once without explanation other than a benchmark result in the cover letter. If you want a chance at getting something merged, please do small and targeted changes with a description and demonstration of their impact

[alvaroaleman]

This aproach actually results in a smaller freelist, since btree.New is just NewWithFreeList(degree, less, NewFreeList[T](DefaultFreeListSize)) under the hood