feat: improve null and bool decoding

[tdakkota]

Valid/bools.json-12           2.14µs ± 2%    1.66µs ± 0%  -22.57%  (p=0.000 n=15+14)
Valid/canada.json-12          3.95ms ± 4%    3.94ms ± 2%     ~     (p=0.878 n=15+11)
Valid/citm_catalog.json-12    1.95ms ± 3%    1.85ms ± 4%   -4.69%  (p=0.000 n=15+15)
Valid/floats.json-12          2.90µs ± 1%    2.96µs ± 1%   +1.99%  (p=0.000 n=15+15)
Valid/large.json-12           49.3µs ± 3%    45.6µs ± 3%   -7.40%  (p=0.000 n=13+14)
Valid/medium.json-12          3.78µs ± 3%    3.58µs ± 3%   -5.27%  (p=0.000 n=15+15)
Valid/nulls.json-12           1.94µs ± 0%    1.51µs ± 0%  -21.91%  (p=0.000 n=13+13)
Valid/otel_ex_1.json-12        607ns ± 2%     652ns ± 7%   +7.52%  (p=0.000 n=15+15)
Valid/small.json-12            353ns ± 3%     357ns ± 1%   +1.15%  (p=0.012 n=14+12)
Valid/twitter.json-12          892µs ± 6%     845µs ± 3%   -5.26%  (p=0.000 n=15+15)

[codecov]

Codecov Report

Merging #18 (cbdf6d5) into main (8242f8a) will decrease coverage by 0.13%.
The diff coverage is 95.16%.

@@            Coverage Diff             @@
##             main      #18      +/-   ##
==========================================
- Coverage   99.50%   99.36%   -0.14%     
==========================================
  Files          29       29              
  Lines        2031     2057      +26     
==========================================
+ Hits         2021     2044      +23     
- Misses          8       10       +2     
- Partials        2        3       +1     

Impacted Files	Coverage Δ
dec.go	98.35% <82.35%> (-1.65%)	⬇️
dec_skip.go	98.44% <100.00%> (+0.05%)	⬆️

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[ernado]

fuzz: elapsed: 29m27s, execs: 83852895 (46575/sec), new interesting: 0 (total: 405)
fuzz: elapsed: 29m30s, execs: 83999235 (48746/sec), new interesting: 0 (total: 405)
fuzz: elapsed: 29m33s, execs: 84162976 (54622/sec), new interesting: 0 (total: 405)
fuzz: elapsed: 29m36s, execs: 84289502 (42175/sec), new interesting: 0 (total: 405)
fuzz: elapsed: 29m39s, execs: 84438027 (49501/sec), new interesting: 0 (total: 405)
fuzz: elapsed: 29m42s, execs: 84587485 (49810/sec), new interesting: 0 (total: 405)
fuzz: elapsed: 29m45s, execs: 84722561 (45030/sec), new interesting: 0 (total: 405)
fuzz: elapsed: 29m48s, execs: 84867400 (48283/sec), new interesting: 0 (total: 405)
fuzz: elapsed: 29m51s, execs: 85002095 (44906/sec), new interesting: 0 (total: 405)
fuzz: elapsed: 29m54s, execs: 85138442 (45448/sec), new interesting: 0 (total: 405)