json_find: make implementation much shorter

[davidhewitt]

This rewrites jiter_json_find to avoid function calls and instead use tight loops to descend the state. Hopefully a win for both simplicity and performance.

[davidhewitt]

It would probably be good to add some benchmarks before we go too much further, but I guess that can wait until after this.

• Codspeed, I assume?

[davidhewitt]

I pushed a starting point for some benchmarks.

When comparing against main, these show a slight improvement from this branch:

json_contains           time:   [39.840 ns 40.145 ns 40.469 ns]
                        change: [-6.1430% -5.1358% -4.1790%] (p = 0.00 < 0.05)
                        Performance has improved.

json_get_str            time:   [55.527 ns 55.875 ns 56.233 ns]
                        change: [-3.8639% -2.8376% -1.6959%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 6 outliers among 100 measurements (6.00%)
  3 (3.00%) high mild
  3 (3.00%) high severe

[samuelcolvin]

Great!