perf: Optimize lower, upper for ASCII inputs

[neilconway]

Which issue does this PR close?

• Closes lower, upper could be further optimized for ASCII-only inputs #21813.

Rationale for this change

This PR implements two optimizations for lower and upper on ASCII strings:

1. For the Utf8/LargeUtf8 code path, we previously did the case conversion via str::to_uppercase or str::to_lowercase. For ASCII inputs, it is a bit faster to use map(u8::to_ascii_lowercase).collect() over the bytes of the string directly: although the stdlib functions are well-optimized, they need to check again on every string to see if it is ASCII. Since we know the input is all-ASCII, we can avoid that check.
2. The Utf8View code path previously wasn't optimized for ASCII strings; add a new code path that is.

Benchmarks (ARM64):

upper

• upper_all_values_are_ascii: 5.4 → 4.1 µs (−24.1%)

lower — all-ASCII (the optimized paths)

• lower_all_values_are_ascii: 1024: 5.4 → 4.0 µs (−25.9%)
• lower_all_values_are_ascii: 4096: 22.6 → 15.6 µs (−31.0%)
• lower_all_values_are_ascii: 8192: 41.9 → 30.8 µs (−26.5%)
• string_views size:4096 str_len:10 null:0 mixed:false: 151.0 → 75.3 µs (−50.1%)
• string_views size:4096 str_len:10 null:0 mixed:true: 175.9 → 134.6 µs (−23.5%)
• string_views size:4096 str_len:10 null:0.1 mixed:false: 143.5 → 76.8 µs (−46.5%)
• string_views size:4096 str_len:10 null:0.1 mixed:true: 166.6 → 125.0 µs (−25.0%)
• string_views size:4096 str_len:64 null:0 mixed:false: 150.1 → 92.7 µs (−38.2%)
• string_views size:4096 str_len:64 null:0 mixed:true: 185.2 → 140.1 µs (−24.4%)
• string_views size:4096 str_len:64 null:0.1 mixed:false: 136.7 → 97.0 µs (−29.0%)
• string_views size:4096 str_len:64 null:0.1 mixed:true: 173.7 → 131.2 µs (−24.5%)
• string_views size:4096 str_len:128 null:0 mixed:false: 190.3 → 141.7 µs (−25.5%)
• string_views size:4096 str_len:128 null:0 mixed:true: 197.0 → 153.7 µs (−22.0%)
• string_views size:4096 str_len:128 null:0.1 mixed:false: 173.3 → 141.7 µs (−18.2%)
• string_views size:4096 str_len:128 null:0.1 mixed:true: 184.0 → 142.8 µs (−22.4%)
• string_views size:8192 str_len:10 null:0 mixed:false: 302.9 → 150.2 µs (−50.4%)
• string_views size:8192 str_len:10 null:0 mixed:true: 352.9 → 279.0 µs (−20.9%)
• string_views size:8192 str_len:10 null:0.1 mixed:false: 285.0 → 154.3 µs (−45.9%)
• string_views size:8192 str_len:10 null:0.1 mixed:true: 334.2 → 266.4 µs (−20.3%)
• string_views size:8192 str_len:64 null:0 mixed:false: 295.6 → 184.4 µs (−37.6%)
• string_views size:8192 str_len:64 null:0 mixed:true: 371.4 → 290.7 µs (−21.7%)
• string_views size:8192 str_len:64 null:0.1 mixed:false: 273.7 → 195.1 µs (−28.7%)
• string_views size:8192 str_len:64 null:0.1 mixed:true: 347.0 → 279.6 µs (−19.4%)
• string_views size:8192 str_len:128 null:0 mixed:false: 379.6 → 285.6 µs (−24.8%)
• string_views size:8192 str_len:128 null:0 mixed:true: 397.1 → 317.4 µs (−20.1%)
• string_views size:8192 str_len:128 null:0.1 mixed:false: 364.1 → 285.1 µs (−21.7%)
• string_views size:8192 str_len:128 null:0.1 mixed:true: 379.3 → 302.3 µs (−20.3%)
• lower_sliced_ascii parent=65536 slice=128 str_len=32: 980.2 → 797.9 ns (−18.6%)

lower — some non-ASCII string_views (mostly noise)

• size:4096 str_len:10 null:0 mixed:false: 374.5 → 362.2 µs (−3.3%)
• size:4096 str_len:10 null:0 mixed:true: 374.6 → 380.5 µs (+1.6%)
• size:4096 str_len:10 null:0.1 mixed:false: 340.8 → 356.5 µs (+4.6%)
• size:4096 str_len:10 null:0.1 mixed:true: 344.0 → 352.5 µs (+2.5%)
• size:4096 str_len:64 null:0 mixed:false: 377.5 → 373.5 µs (−1.1%)
• size:4096 str_len:64 null:0 mixed:true: 380.6 → 375.0 µs (−1.5%)
• size:4096 str_len:64 null:0.1 mixed:false: 330.7 → 341.8 µs (+3.4%)
• size:4096 str_len:64 null:0.1 mixed:true: 341.8 → 354.2 µs (+3.6%)
• size:4096 str_len:128 null:0 mixed:false: 371.8 → 356.2 µs (−4.2%)
• size:4096 str_len:128 null:0 mixed:true: 378.9 → 386.0 µs (+1.9%)
• size:4096 str_len:128 null:0.1 mixed:false: 350.5 → 350.3 µs (−0.1%)
• size:4096 str_len:128 null:0.1 mixed:true: 351.0 → 337.9 µs (−3.7%)
• size:8192 str_len:10 null:0 mixed:false: 740.0 → 757.2 µs (+2.3%)
• size:8192 str_len:10 null:0 mixed:true: 781.3 → 750.2 µs (−4.0%)
• size:8192 str_len:10 null:0.1 mixed:false: 693.7 → 693.7 µs (0.0%)
• size:8192 str_len:10 null:0.1 mixed:true: 681.5 → 705.2 µs (+3.5%)
• size:8192 str_len:64 null:0 mixed:false: 755.5 → 768.6 µs (+1.7%)
• size:8192 str_len:64 null:0 mixed:true: 759.6 → 754.3 µs (−0.7%)
• size:8192 str_len:64 null:0.1 mixed:false: 711.5 → 667.8 µs (−6.1%)
• size:8192 str_len:64 null:0.1 mixed:true: 682.1 → 688.2 µs (+0.9%)
• size:8192 str_len:128 null:0 mixed:false: 771.5 → 765.9 µs (−0.7%)
• size:8192 str_len:128 null:0 mixed:true: 747.7 → 792.6 µs (+6.0%)
• size:8192 str_len:128 null:0.1 mixed:false: 687.1 → 701.3 µs (+2.1%)
• size:8192 str_len:128 null:0.1 mixed:true: 679.2 → 696.8 µs (+2.6%)

lower — first/middle non-ASCII (flat)

• lower_the_first_value_is_nonascii: 1024: 42.1 → 42.4 µs (+0.7%)
• lower_the_first_value_is_nonascii: 4096: 173.9 → 173.3 µs (−0.3%)
• lower_the_first_value_is_nonascii: 8192: 350.8 → 349.3 µs (−0.4%)
• lower_the_middle_value_is_nonascii: 1024: 42.9 → 42.8 µs (−0.2%)
• lower_the_middle_value_is_nonascii: 4096: 175.1 → 176.3 µs (+0.7%)
• lower_the_middle_value_is_nonascii: 8192: 353.6 → 354.6 µs (+0.3%)

What changes are included in this PR?

• Implement optimizations
• Share StringViewArray buffer size constants with the bulk-NULL builders

Are these changes tested?

Covered by existing tests.

Are there any user-facing changes?

No.

[comphead]

lets add some comments, I assume 12 len is the fast path for german strings?

[comphead]

Thanks @neilconway
I believe the optimization tightly connected to german strings specifics and it would be nice to comment the byte level work