Faster DNS name validation

[djc]

While looking at benchmark results for

• conn: simplify message writing path rustls#3163

I noticed that rustls_pki_types::server_name::validate() was more expensive than I expected. Worked with Claude to optimize it (and verify that it has the same results). Criterion results from this improvement:

     Running benches/dns_name.rs (target/release/deps/dns_name-bef6433e6c7ace85)
Gnuplot not found, using plotters backend
dns_name/typical        time:   [124.84 ns 125.63 ns 126.45 ns]
                        change: [−55.558% −55.144% −54.712%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) high mild
dns_name/ip_like_rejected
                        time:   [20.163 ns 20.318 ns 20.484 ns]
                        change: [−27.528% −26.440% −25.354%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 3 outliers among 100 measurements (3.00%)
  3 (3.00%) high mild
dns_name/max_length     time:   [132.86 ns 137.70 ns 143.23 ns]
                        change: [−68.711% −67.456% −66.337%] (p = 0.00 < 0.05)
                        Performance has improved.

[ctz]

Can we have both the performance the formal state-machine type? What happens if we have the state machine type without the large fields?

[djc]

Can we have both the performance the formal state-machine type? What happens if we have the state machine type without the large fields?

Here's a new version that I largely wrote myself. It's a little faster still:

dns_name/typical        time:   [101.92 ns 102.61 ns 103.32 ns]
                        change: [−63.516% −63.198% −62.871%] (p = 0.00 < 0.05)
                        Performance has improved.
dns_name/ip_like_rejected
                        time:   [14.064 ns 14.223 ns 14.412 ns]
                        change: [−46.518% −45.556% −44.498%] (p = 0.00 < 0.05)
                        Performance has improved.
dns_name/max_length     time:   [126.00 ns 126.60 ns 127.36 ns]
                        change: [−74.322% −74.016% −73.717%] (p = 0.00 < 0.05)
                        Performance has improved.