Optimize unmarshal type handling

[Sean-Der]

Dispatch type as a byte, instead of allocating a string

Before
'''
14433 ns/op 2576 B/op 108 allocs/op
'''

After
'''
13616 ns/op 2512 B/op 83 allocs/op
'''

[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 26 lines in your changes are missing coverage. Please review.

Project coverage is 64.22%. Comparing base (37a57e6) to head (1322d2c).
Report is 1 commits behind head on master.

Files	Patch %	Lines
unmarshal.go	71.60%	23 Missing ⚠️
base_lexer.go	66.66%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #174      +/-   ##
==========================================
- Coverage   64.28%   64.22%   -0.07%     
==========================================
  Files          11       11              
  Lines        1540     1526      -14     
==========================================
- Hits          990      980      -10     
+ Misses        449      446       -3     
+ Partials      101      100       -1     

Flag	Coverage Δ
go	64.22% <71.42%> (-0.07%)	⬇️
wasm	64.22% <71.42%> (-0.07%)	⬇️

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