fix: decimal map key may be truncated and populated unexpectedly

[AsterDY]

Bugfix

fix #381

Feature

add options to make default buffer size adjustable

• option.DefaultDecoderBufferSize: the initial buffer size of StreamDecoder
• option.DefaultEncoderBufferSize: the initial buffer size of Encoder

Opt

adjust both DefaultDecoderBufferSize and DefaultEncoderBufferSize as 128KB

• benchmark result show improvement on both CPU and MEM

name                                    old time/op    new time/op    delta
Encoder_Parallel_Generic_Sonic-16         18.0µs ±25%    16.6µs ±27%     ~     (p=0.247 n=10+10)
Encoder_Parallel_Binding_Sonic-16         2.37µs ±21%    2.43µs ±15%     ~     (p=0.796 n=9+9)
Encoder_Parallel_Binding_Sonic_Fast-16    1.93µs ± 4%    1.85µs ±26%     ~     (p=1.000 n=10+10)
Encoder_Generic_Sonic-16                  41.4µs ± 8%    37.0µs ± 2%  -10.51%  (p=0.000 n=10+9)
Encoder_Generic_Sonic_Fast-16             29.0µs ± 7%    25.5µs ± 3%  -11.94%  (p=0.000 n=10+10)
Encoder_Parallel_Generic_Sonic_Fast-16    11.0µs ± 6%     9.1µs ± 7%  -16.86%  (p=0.000 n=10+10)
Encoder_Binding_Sonic-16                  7.73µs ± 6%    6.38µs ± 2%  -17.47%  (p=0.000 n=10+10)
Encoder_Binding_Sonic_Fast-16             6.72µs ± 2%    5.26µs ± 3%  -21.72%  (p=0.000 n=10+10)

name                                    old speed      new speed      delta
Encoder_Parallel_Generic_Sonic-16        741MB/s ±31%   806MB/s ±33%     ~     (p=0.247 n=10+10)
Encoder_Parallel_Binding_Sonic-16       5.55GB/s ±18%  5.40GB/s ±14%     ~     (p=0.796 n=9+9)
Encoder_Parallel_Binding_Sonic_Fast-16  6.77GB/s ± 5%  6.92GB/s ±20%     ~     (p=0.720 n=10+9)
Encoder_Generic_Sonic-16                 316MB/s ± 9%   352MB/s ± 2%  +11.46%  (p=0.000 n=10+9)
Encoder_Generic_Sonic_Fast-16            452MB/s ± 7%   511MB/s ± 3%  +13.23%  (p=0.000 n=10+10)
Encoder_Parallel_Generic_Sonic_Fast-16  1.19GB/s ± 6%  1.43GB/s ± 7%  +20.27%  (p=0.000 n=10+10)
Encoder_Binding_Sonic-16                1.69GB/s ± 6%  2.04GB/s ± 2%  +21.07%  (p=0.000 n=10+10)
Encoder_Binding_Sonic_Fast-16           1.94GB/s ± 2%  2.48GB/s ± 3%  +27.78%  (p=0.000 n=10+10)

name                                    old alloc/op   new alloc/op   delta
Encoder_Parallel_Generic_Sonic-16         14.0kB ± 0%    13.9kB ± 1%     ~     (p=0.218 n=9+10)
Encoder_Parallel_Binding_Sonic-16         14.1kB ± 1%    14.1kB ± 2%     ~     (p=0.896 n=10+10)
Encoder_Parallel_Binding_Sonic_Fast-16    9.93kB ± 2%    9.88kB ± 3%     ~     (p=0.393 n=10+10)
Encoder_Parallel_Generic_Sonic_Fast-16    9.82kB ± 1%    9.70kB ± 0%   -1.23%  (p=0.000 n=10+10)
Encoder_Generic_Sonic-16                  14.2kB ± 1%    13.8kB ± 0%   -2.97%  (p=0.000 n=9+9)
Encoder_Generic_Sonic_Fast-16             10.1kB ± 1%     9.7kB ± 0%   -3.76%  (p=0.000 n=9+10)
Encoder_Binding_Sonic_Fast-16             10.3kB ± 1%     9.8kB ± 0%   -4.72%  (p=0.000 n=9+10)
Encoder_Binding_Sonic-16                  14.9kB ± 1%    14.1kB ± 0%   -5.20%  (p=0.000 n=10+9)

name                                    old allocs/op  new allocs/op  delta
Encoder_Generic_Sonic-16                    4.00 ± 0%      4.00 ± 0%     ~     (all equal)
Encoder_Generic_Sonic_Fast-16               4.00 ± 0%      4.00 ± 0%     ~     (all equal)
Encoder_Binding_Sonic-16                    4.00 ± 0%      4.00 ± 0%     ~     (all equal)
Encoder_Binding_Sonic_Fast-16               4.00 ± 0%      4.00 ± 0%     ~     (all equal)
Encoder_Parallel_Generic_Sonic-16           4.00 ± 0%      4.00 ± 0%     ~     (all equal)
Encoder_Parallel_Generic_Sonic_Fast-16      4.00 ± 0%      4.00 ± 0%     ~     (all equal)
Encoder_Parallel_Binding_Sonic-16           4.00 ± 0%      4.00 ± 0%     ~     (all equal)
Encoder_Parallel_Binding_Sonic_Fast-16      4.00 ± 0%      4.00 ± 0%     ~     (all equal)