perf: use sentinel error for theta sketch hashtable.

[proost]

Go vs Java benchmark: apache/datasketches-characterization#89

code:

func BenchmarkHashAndScreen(b *testing.B) {
	b.Run("most hashes passes", func(b *testing.B) {
		ht := NewHashtable(10, 10, ResizeX2, 1.0, MaxTheta, DefaultSeed, true)
		b.ReportAllocs()
		b.ResetTimer()
		for i := 0; i < b.N; i++ {
			_, _ = ht.HashInt64AndScreen(int64(i))
		}
	})

	b.Run("hashes exceed theta", func(b *testing.B) {
		ht := NewHashtable(10, 10, ResizeX2, 0.001, 1000, DefaultSeed, true)
		b.ReportAllocs()
		b.ResetTimer()
		for i := 0; i < b.N; i++ {
			_, _ = ht.HashInt64AndScreen(int64(i))
		}
	})
}

• current code performance:

goos: darwin
goarch: arm64
pkg: github.com/apache/datasketches-go/theta
cpu: Apple M1 Pro
BenchmarkHashAndScreen
BenchmarkHashAndScreen/most_hashes_passes
BenchmarkHashAndScreen/most_hashes_passes-10         	240147729	         5.022 ns/op	       0 B/op	       0 allocs/op
BenchmarkHashAndScreen/hashes_exceed_theta
BenchmarkHashAndScreen/hashes_exceed_theta-10        	 9001977	       132.9 ns/op	      96 B/op	       4 allocs/op

• changed:

goos: darwin
goarch: arm64
pkg: github.com/apache/datasketches-go/theta
cpu: Apple M1 Pro
BenchmarkHashAndScreen
BenchmarkHashAndScreen/most_hashes_passes
BenchmarkHashAndScreen/most_hashes_passes-10         	241465656	         4.943 ns/op	       0 B/op	       0 allocs/op
BenchmarkHashAndScreen/hashes_exceed_theta
BenchmarkHashAndScreen/hashes_exceed_theta-10        	246932887	         4.860 ns/op	       0 B/op	       0 allocs/op

Sorry for not considering performance in hot path when i wrote code and Thank you for accepting breaking change.

[freakyzoidberg]

Don't be sorry, thanks for the time you put into this!