feat: optimize gridDisksUnsafe implementation

[justinhwang]

goos: darwin
goarch: arm64
pkg: github.com/uber/h3-go/v4
cpu: Apple M3 Max
                   │ /tmp/before.txt │          /tmp/after.txt          │
                   │     sec/op      │   sec/op    vs base              │
GridDisksUnsafe-16        3.150 ± 4%   2.957 ± 5%  -6.12% (p=0.004 n=6)

                   │ /tmp/before.txt │           /tmp/after.txt           │
                   │      B/op       │     B/op      vs base              │
GridDisksUnsafe-16      1.708Gi ± 0%   1.683Gi ± 0%  -1.47% (p=0.002 n=6)

                   │ /tmp/before.txt │            /tmp/after.txt             │
                   │    allocs/op    │   allocs/op    vs base                │
GridDisksUnsafe-16   676168.000 ± 0%   2.000 ± 1200%  -100.00% (p=0.002 n=6)

[coveralls]

Pull Request Test Coverage Report for Build 23510145703

Details

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 23508937904:	0.0%
Covered Lines:	781
Relevant Lines:	781

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💛 - Coveralls