feat: Use a bitset to represent the set of transformations

[Dr-Emann]

This is a breaking change from the rust side, at least, since it changes publicly exported types (LhsTransformations and the transformations field of the Lhs type), so I bumped the version to 2.0. I'm not sure if we should really be exposing all these types and fields publicly (or if we even consider the rust API part of semver).

This has a mild but consistent perf improvement with the benchmarks:

     Running benches/build.rs (target/release/deps/build-7c4a2d11080689ae)
Build Router            time:   [3.5907 ms 3.5968 ms 3.6035 ms]
                        change: [−4.3578% −4.0135% −3.6584%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 2 outliers among 100 measurements (2.00%)
  1 (1.00%) high mild
  1 (1.00%) high severe

     Running benches/match_mix.rs (target/release/deps/match_mix-ad74be14abd29154)
Match                   time:   [75.501 ns 75.606 ns 75.721 ns]
                        change: [−2.5543% −2.2070% −1.8833%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 9 outliers among 100 measurements (9.00%)
  4 (4.00%) high mild
  5 (5.00%) high severe

Doesn't Match           time:   [15.672 ms 15.712 ms 15.752 ms]
                        change: [−34.306% −34.101% −33.937%] (p = 0.00 < 0.05)
                        Performance has improved.

[StarlightIbuki]

LGTM. I do not yet have time for an accurate bench. Maybe later, I will add a report of its improvement on Kong's overall performance.