feat: improve string

[quagmt]

Description

• Optimize String with table lookup method
• Remove byte pre-allocation because it's likely to be optimized by the compiler anyways
• Benchmark before and after

goos: linux
goarch: amd64
pkg: github.com/quagmt/udecimal/benchmarks
cpu: Intel(R) Core(TM) i9-14900HX
                                                       │     old      │               udecimal               │
                                                       │    sec/op    │    sec/op     vs base                │
String/udec/1234567890123456789.1234567890123456879-32   88.52n ±  6%   77.35n ± 10%  -12.61% (p=0.000 n=10)
String/udec/123-32                                       15.54n ± 10%   14.22n ±  4%   -8.52% (p=0.000 n=10)
String/udec/123456.123456-32                             35.95n ±  5%   31.49n ± 11%  -12.41% (p=0.000 n=10)
String/udec/1234567890-32                                33.29n ±  8%   30.60n ±  8%   -8.09% (p=0.009 n=10)
String/udec/0.1234567890123456879-32                     48.91n ±  8%   42.60n ±  6%  -12.91% (p=0.000 n=10)
String/udec/12345.1234567890123456789-32                 61.08n ±  5%   51.02n ±  8%  -16.47% (p=0.000 n=10)
geomean                                                  41.24n         36.34n        -11.88%

                                                       │    old     │               udecimal               │
                                                       │    B/op    │    B/op     vs base                  │
String/udec/1234567890123456789.1234567890123456879-32   48.00 ± 0%   48.00 ± 0%        ~ (p=1.000 n=10) ¹
String/udec/123-32                                       5.000 ± 0%   3.000 ± 0%  -40.00% (p=0.000 n=10)
String/udec/123456.123456-32                             16.00 ± 0%   16.00 ± 0%        ~ (p=1.000 n=10) ¹
String/udec/1234567890-32                                16.00 ± 0%   16.00 ± 0%        ~ (p=1.000 n=10) ¹
String/udec/0.1234567890123456879-32                     24.00 ± 0%   24.00 ± 0%        ~ (p=1.000 n=10) ¹
String/udec/12345.1234567890123456789-32                 32.00 ± 0%   32.00 ± 0%        ~ (p=1.000 n=10) ¹
geomean                                                  19.01        17.46        -8.16%
¹ all samples are equal

                                                       │    old     │              udecimal               │
                                                       │ allocs/op  │ allocs/op   vs base                 │
String/udec/1234567890123456789.1234567890123456879-32   1.000 ± 0%   1.000 ± 0%       ~ (p=1.000 n=10) ¹
String/udec/123-32                                       1.000 ± 0%   1.000 ± 0%       ~ (p=1.000 n=10) ¹
String/udec/123456.123456-32                             1.000 ± 0%   1.000 ± 0%       ~ (p=1.000 n=10) ¹
String/udec/1234567890-32                                1.000 ± 0%   1.000 ± 0%       ~ (p=1.000 n=10) ¹
String/udec/0.1234567890123456879-32                     1.000 ± 0%   1.000 ± 0%       ~ (p=1.000 n=10) ¹
String/udec/12345.1234567890123456789-32                 1.000 ± 0%   1.000 ± 0%       ~ (p=1.000 n=10) ¹
geomean                                                  1.000        1.000       +0.00%
¹ all samples are equal

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.79%. Comparing base (1d8c752) to head (f14245b).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #19      +/-   ##
==========================================
+ Coverage   95.74%   95.79%   +0.04%     
==========================================
  Files           5        5              
  Lines        1693     1711      +18     
==========================================
+ Hits         1621     1639      +18     
  Misses         48       48              
  Partials       24       24              

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