Assume most parsing options aren't set

Same strategy used for the generator, if we assume only
a couple options are passed at most, we might as well
traverse the option hash rather than to check all possible
keys.

```
== Parsing small hash (65 bytes)
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [arm64-darwin23]
Warming up --------------------------------------
                json   229.732k i/100ms
                  oj   221.571k i/100ms
           oj strict   255.080k i/100ms
          Oj::Parser   427.514k i/100ms
           rapidjson   282.252k i/100ms
Calculating -------------------------------------
                json      2.185M (± 3.3%) i/s  (457.68 ns/i) -     11.027M in   5.052670s
                  oj      2.227M (± 0.4%) i/s  (449.10 ns/i) -     11.300M in   5.074920s
           oj strict      2.532M (± 1.4%) i/s  (394.97 ns/i) -     12.754M in   5.038527s
          Oj::Parser      4.309M (± 0.5%) i/s  (232.10 ns/i) -     21.803M in   5.060621s
           rapidjson      2.811M (± 0.2%) i/s  (355.78 ns/i) -     14.113M in   5.020940s

Comparison:
                json:  2184913.9 i/s
          Oj::Parser:  4308534.8 i/s - 1.97x  faster
           rapidjson:  2810757.1 i/s - 1.29x  faster
           oj strict:  2531841.6 i/s - 1.16x  faster
                  oj:  2226694.4 i/s - same-ish: difference falls within error
```

Author: byroot