feat: implement CharRefTokenizer

[kkebo]

Description

I've implemented CharRefTokenizer.

Benchmark Results

$ swift package --package-path Benchmarks benchmark baseline compare main
warning: 'package-benchmark': Jemalloc disabled through environment variable.
Building for debugging...
[9/9] Emitting module BenchmarkBoilerplateGenerator
Build of product 'BenchmarkBoilerplateGenerator' complete! (1.32s)
Building for debugging...
[1/1] Write swift-version--FC39A71C9A0968F.txt
Build of product 'BenchmarkTool' complete! (2.12s)
Build complete!
Building BenchmarkTool in release mode...
Building benchmark targets in release mode for benchmark run...
Building MyBenchmark

==================
Running Benchmarks
==================

100% [------------------------------------------------------------] ETA: 00:00:00 | MyBenchmark:TokenizerBenchmark

===================================================
Comparing results between 'main' and 'Current_run'
===================================================

Host 'Brown-rhinoceros-beetle' with 8 'aarch64' processors with 7 GB memory, running:
#1 SMP PREEMPT_DYNAMIC Sun Mar 24 19:44:17 UTC 2024

MyBenchmark
============================================================================================================================

----------------------------------------------------------------------------------------------------------------------------
TokenizerBenchmark metrics
----------------------------------------------------------------------------------------------------------------------------

╒══════════════════════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│         Time (wall clock) (μs) *         │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│                   main                   │      12 │      12 │      12 │      12 │      13 │      20 │      20 │      80 │
├──────────────────────────────────────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│               Current_run                │      12 │      12 │      12 │      13 │      13 │      15 │      15 │      81 │
├──────────────────────────────────────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│                    Δ                     │       0 │       0 │       0 │       1 │       0 │      -5 │      -5 │       1 │
├──────────────────────────────────────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│              Improvement %               │       0 │       0 │       0 │      -8 │       0 │      25 │      25 │       1 │
╘══════════════════════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

╒══════════════════════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│          Throughput (# / s) (K)          │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│                   main                   │      82 │      82 │      81 │      81 │      79 │      49 │      49 │      80 │
├──────────────────────────────────────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│               Current_run                │      82 │      81 │      81 │      79 │      79 │      65 │      65 │      81 │
├──────────────────────────────────────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│                    Δ                     │       0 │      -1 │       0 │      -2 │       0 │      16 │      16 │       1 │
├──────────────────────────────────────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│              Improvement %               │       0 │      -1 │       0 │      -2 │       0 │      33 │      33 │       1 │
╘══════════════════════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

[github-actions]

Code Metrics Report

	main (e55b299)	#39 (3a31200)	+/-
Coverage	88.9%	88.7%	-0.1%

Details

  |           | main (e55b299) | #39 (3a31200) |  +/-  |
  |-----------|----------------|---------------|-------|
- | Coverage  |          88.9% |         88.7% | -0.1% |
  |   Files   |              7 |             8 |    +1 |
  |   Lines   |           1202 |          1258 |   +56 |
+ |   Covered |           1068 |          1116 |   +48 |

Code coverage of files in pull request scope (88.6% → 88.4%)

Files	Coverage	+/-
Sources/HTMLEntities/namedChars.swift	100.0%	+100.0%
Sources/Tokenizer/CharRefTokenizer.swift	97.7%	+0.0%
Sources/Tokenizer/Tokenizer.swift	86.3%	-0.7%

---

Reported by octocov

[kkebo]

LGTM