perf: inline binary search

[stevenh]

Use inline version of binary search instead of sort.Search which is ~50% quicker in most cases.

benchstat -filter '.unit:ns/op' orig.log inline.log goos: linux
goarch: amd64
pkg: github.com/hashicorp/go-immutable-radix/v2
cpu: Intel(R) Core(TM) i9-14900HX
                                              │   orig.log    │             inline.log             │
                                              │    sec/op     │   sec/op     vs base               │
LongestPrefix/words-exact-match-early-32         59.47n ± 12%   29.70n ± 1%  -50.06% (p=0.002 n=6)
LongestPrefix/words-exact-match-late-32          56.99n ±  2%   33.43n ± 3%  -41.35% (p=0.002 n=6)
LongestPrefix/words-prefix-match-early-32       106.85n ±  3%   52.09n ± 2%  -51.24% (p=0.002 n=6)
LongestPrefix/words-prefix-match-late-32         75.12n ±  2%   38.78n ± 2%  -48.37% (p=0.002 n=6)
LongestPrefix/words-not-found-early-32          12.945n ±  2%   5.267n ± 3%  -59.31% (p=0.002 n=6)
LongestPrefix/words-not-found-late-32           12.415n ±  2%   4.577n ± 4%  -63.13% (p=0.002 n=6)
LongestPrefix/uuids-exact-match-early-32         61.14n ±  4%   33.76n ± 7%  -44.78% (p=0.002 n=6)
LongestPrefix/uuids-exact-match-late-32          60.79n ±  4%   35.28n ± 6%  -41.96% (p=0.002 n=6)
LongestPrefix/uuids-prefix-match-early-32        57.02n ±  8%   32.57n ± 4%  -42.87% (p=0.002 n=6)
LongestPrefix/uuids-prefix-match-late-32         58.01n ±  2%   34.44n ± 3%  -40.63% (p=0.002 n=6)
LongestPrefix/uuids-not-found-early-32           48.36n ±  3%   30.74n ± 3%  -36.44% (p=0.002 n=6)
LongestPrefix/uuids-not-found-late-32           11.600n ±  4%   4.099n ± 6%  -64.66% (p=0.002 n=6)
LongestPrefix/endpoints-exact-match-early-32     57.82n ±  4%   34.01n ± 3%  -41.18% (p=0.002 n=6)
LongestPrefix/endpoints-exact-match-late-32      73.75n ±  4%   41.46n ± 3%  -43.77% (p=0.002 n=6)
LongestPrefix/endpoints-prefix-match-early-32    51.55n ±  4%   30.58n ± 1%  -40.69% (p=0.002 n=6)
LongestPrefix/endpoints-prefix-match-late-32     63.00n ±  4%   40.37n ± 4%  -35.92% (p=0.002 n=6)
LongestPrefix/endpoints-not-found-early-32       6.098n ±  4%   2.606n ± 6%  -57.26% (p=0.002 n=6)
LongestPrefix/endpoints-not-found-late-32        6.188n ±  3%   2.646n ± 3%  -57.23% (p=0.002 n=6)
geomean                                          36.86n         18.93n       -48.63%

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