unwrapping slice makes it easier to see what is happening in these
algorithms and makes it easier to optimize. Additionally this makes
these functions usable without having to wrap them into a slice.

Benchmark (benchmarkCompareUtf16BE, length=1000):

- ascii=true: 3.483 -> 0.102 ns/codepoint

- ascii=false: 8.214 -> 6.395 ns/codepoint

Benchmark (benchmarkReverse, length=1000):

- ascii=true: 0.318 -> 0.067 ns/codepoint

- ascii=false: 3.397 -> 3.406 ns/codepoint (flat within noise)

Benchmark (benchmarkToUpperCase, length=1000):

- ascii=true: 3.053 -> 0.601 ns/codepoint

- ascii=false: 7.254 -> 5.019 ns/codepoint

Benchmark (benchmarkToLowerCase, length=1000):

- ascii=true: 3.029 -> 0.501 ns/codepoint

- ascii=false: 7.145 -> 4.183 ns/codepoint

Benchmark (benchmarkFixInvalidUtf8WithoutReplacement, inputLength=1024):

- valid_non_ascii: 6.341 -> 3.978 ns/byte

- invalid_non_ascii: 6.242 -> 4.549 ns/byte

Benchmark (benchmarkLeftTrim, length=1000):

- ascii=true: 1.919 -> 0.344 ns/codepoint

- ascii=false: 3.137 -> 2.201 ns/codepoint

Benchmark (benchmarkRightTrim, length=1000):

- ascii=true: 0.551 -> 0.359 ns/codepoint

- ascii=false: 2.939 -> 2.534 ns/codepoint

Benchmark (benchmarkTrimCustom, length=1000):

- ascii=true: 2.702 -> 0.474 ns/codepoint

- ascii=false: 5.224 -> 4.329 ns/codepoint

Benchmark (benchmarkSetCodePointAt, length=1000):

- ascii=true: 0.336 -> 0.332 ns/codepoint

- ascii=false: 2.259 -> 2.334 ns/codepoint

Related benchmark (benchmarkCodePointToUtf8, length=1000):

- ascii=false: 2.404 -> 2.154 ns/codepoint

Useful for Trino VARCHAR->code points casts and similar decode loops.

Benchmark (ns/byte, length=1000):

- toCodePointsApi ascii: 0.2319 (baseline two-pass: 2.4902)

- toCodePointsApi non-ascii: 1.0820 (baseline two-pass: 1.6643)

Adds fromCodePoints to encode code-point arrays directly into UTF-8
Slice output. This is useful for Trino-style loops that currently
pre-size and encode with repeated setCodePointAt calls.

Benchmark (SliceUtf8Benchmark, length=1000 code points):

- ascii=true: fromCodePointsApi 0.326 ns/codepoint vs Trino baseline 0.500 ns/codepoint

- ascii=false: fromCodePointsApi 2.062 ns/codepoint vs Trino baseline 3.230 ns/codepoint

Adds codePointByteLengths so callers can decode UTF-8 once and directly
materialize per-code-point byte widths (1..4) for padding/loop planning.

Benchmark (SliceUtf8Benchmark, length=128 code points):

- ascii=true: helper(byte[]) 0.696 ns/codepoint vs Trino byte[] baseline 1.020 ns/codepoint

- ascii=false: helper(byte[]) 2.129 ns/codepoint vs Trino byte[] baseline 3.596 ns/codepoint