perf: remove allocation in CM sketch

[proost]

we can reduce allocating of slices to on-heap

If run the escape analysis,

count/count_min_sketch.go:97:31: make([]int64, c.numHashes) escapes to heap in (*CountMinSketch).getHashes:

Before:

goos: darwin
goarch: arm64
pkg: github.com/apache/datasketches-go/count
cpu: Apple M4 Pro
BenchmarkCountMinSketch_Update
BenchmarkCountMinSketch_Update-12    	34135192	        32.77 ns/op	      24 B/op	       1 allocs/op
PASS


goos: darwin
goarch: arm64
pkg: github.com/apache/datasketches-go/count
cpu: Apple M4 Pro
BenchmarkCountMinSketch_GetEstimate
BenchmarkCountMinSketch_GetEstimate-12    	34794710	        32.60 ns/op	      24 B/op	       1 allocs/op
PASS

After:

goos: darwin
goarch: arm64
pkg: github.com/apache/datasketches-go/count
cpu: Apple M4 Pro
BenchmarkCountMinSketch_Update
BenchmarkCountMinSketch_Update-12    	45174462	        26.34 ns/op	       0 B/op	       0 allocs/op
PASS

goos: darwin
goarch: arm64
pkg: github.com/apache/datasketches-go/count
cpu: Apple M4 Pro
BenchmarkCountMinSketch_GetEstimate
BenchmarkCountMinSketch_GetEstimate-12    	45396912	        26.71 ns/op	       0 B/op	       0 allocs/op
PASS