CI: ci.yml - update to actions/checkout@v4

Added automated update workflow for GitHub Actions

This way they're hidden in diffs.

It would be good to enforce on CI that the generated files match
the source change, however ragel's output isn't consistent
across versions and system, so we'll have to rely on changes
being noticed by further contributions.

Mark parser.c and Parser.java as generated files

Before this commit, we would try to scan for a float, then if that
failed, scan for an integer.  But floats and integers have many bytes in
common, so we would end up scanning the same bytes multiple times.

This patch combines integer and float scanning machines so that we only
have to scan bytes once.  If the machine finds "float parts", then it
executes the "isFloat" transition in the machine, which sets a boolean
letting us know that the parser found a float.

If we didn't find a float, but we did match, then we know it's an int.

Reduce comparisons when parsing numbers

Fix: #697

This way even if `Encoding.default_external` is set to a weird value
the document will be parsed just fine.

JSON.load_file: explictly load the file as UTF-8

The documentation state `Oj::Parser.usual` isn't thread safe:
https://github.com/ohler55/oj/blob/c70bf4125b546bc7146840b15de36460d42b4dff/ext/oj/parser.c#L1507-L1513

As such we shouldn't benchark it this way, but instantiate a new
parser every time. Technically in real world scenarios you could
create a pool of parsers and re-use them, but if it's not provided
by the gem, I'm not sure we should go out of our way to do it.

Benchmark `Oj::Parser` in a thread safe way

Fix $VERBOSE restore

Otherwise the likeliness of seeing that key again is really low, and looking up
the cache is just a waste.

Before:

```
== Parsing small hash (65 bytes)
ruby 3.4.0dev (2024-11-13T12:32:57Z fstr-update-callba.. 9b44b455b3) +YJIT +PRISM [arm64-darwin24]
Warming up --------------------------------------
                json   343.049k i/100ms
                  oj   213.943k i/100ms
          Oj::Parser    31.583k i/100ms
           rapidjson   303.433k i/100ms
Calculating -------------------------------------
                json      3.704M (± 1.5%) i/s  (270.01 ns/i) -     18.525M in   5.003078s
                  oj      2.200M (± 1.1%) i/s  (454.46 ns/i) -     11.125M in   5.056526s
          Oj::Parser    285.369k (± 4.8%) i/s    (3.50 μs/i) -      1.453M in   5.103866s
           rapidjson      3.216M (± 1.6%) i/s  (310.95 ns/i) -     16.082M in   5.001973s

Comparison:
                json:  3703517.4 i/s
           rapidjson:  3215983.0 i/s - 1.15x  slower
                  oj:  2200417.1 i/s - 1.68x  slower
          Oj::Parser:   285369.1 i/s - 12.98x  slower

== Parsing test from oj (258 bytes)
ruby 3.4.0dev (2024-11-13T12:32:57Z fstr-update-callba.. 9b44b455b3) +YJIT +PRISM [arm64-darwin24]
Warming up --------------------------------------
                json    54.539k i/100ms
                  oj    41.473k i/100ms
          Oj::Parser    24.064k i/100ms
           rapidjson    51.466k i/100ms
Calculating -------------------------------------
                json    549.386k (± 1.6%) i/s    (1.82 μs/i) -      2.781M in   5.064316s
                  oj    417.003k (± 1.3%) i/s    (2.40 μs/i) -      2.115M in   5.073047s
          Oj::Parser    226.500k (± 4.7%) i/s    (4.42 μs/i) -      1.131M in   5.005466s
           rapidjson    526.124k (± 1.0%) i/s    (1.90 μs/i) -      2.676M in   5.087176s

Comparison:
                json:   549385.6 i/s
           rapidjson:   526124.3 i/s - 1.04x  slower
                  oj:   417003.4 i/s - 1.32x  slower
          Oj::Parser:   226500.4 i/s - 2.43x  slower
```

After:

```
== Parsing small hash (65 bytes)
ruby 3.4.0dev (2024-11-13T12:32:57Z fstr-update-callba.. 9b44b455b3) +YJIT +PRISM [arm64-darwin24]
Warming up --------------------------------------
                json   361.394k i/100ms
                  oj   217.203k i/100ms
          Oj::Parser    28.855k i/100ms
           rapidjson   303.404k i/100ms
Calculating -------------------------------------
                json      3.859M (± 2.9%) i/s  (259.13 ns/i) -     19.515M in   5.061302s
                  oj      2.191M (± 1.6%) i/s  (456.49 ns/i) -     11.077M in   5.058043s
          Oj::Parser    315.132k (± 7.1%) i/s    (3.17 μs/i) -      1.587M in   5.065707s
           rapidjson      3.156M (± 4.0%) i/s  (316.88 ns/i) -     15.777M in   5.008949s

Comparison:
                json:  3859046.5 i/s
           rapidjson:  3155778.5 i/s - 1.22x  slower
                  oj:  2190616.0 i/s - 1.76x  slower
          Oj::Parser:   315132.4 i/s - 12.25x  slower

== Parsing test from oj (258 bytes)
ruby 3.4.0dev (2024-11-13T12:32:57Z fstr-update-callba.. 9b44b455b3) +YJIT +PRISM [arm64-darwin24]
Warming up --------------------------------------
                json    55.682k i/100ms
                  oj    40.343k i/100ms
          Oj::Parser    25.119k i/100ms
           rapidjson    51.500k i/100ms
Calculating -------------------------------------
                json    555.808k (± 1.4%) i/s    (1.80 μs/i) -      2.784M in   5.010092s
                  oj    412.283k (± 1.7%) i/s    (2.43 μs/i) -      2.098M in   5.089900s
          Oj::Parser    279.306k (±13.3%) i/s    (3.58 μs/i) -      1.356M in   5.022079s
           rapidjson    517.177k (± 2.7%) i/s    (1.93 μs/i) -      2.626M in   5.082352s

Comparison:
                json:   555808.3 i/s
           rapidjson:   517177.1 i/s - 1.07x  slower
                  oj:   412283.2 i/s - 1.35x  slower
          Oj::Parser:   279306.5 i/s - 1.99x  slower
```

Only use the key cache if the Hash is in an Array

Fix redundant to_str call in JSON.[] method