opt: refactor streaming decoder to fully use buffer

[AsterDY]

Optimization

• refactor implementation of StreamDecoder.Decode()
• reduce memory copy by limiting start and end of slice passed to skip()
• never move head of decoder buffer, always move tail
• check if buffer remains valid bytes after eachDecode() or More(), if not, recycle buffer

Benchmark

name                          old time/op    new time/op    delta
DecodeStream_Sonic/halt-16       698µs ± 7%     732µs ± 3%   +4.84%  (p=0.002 n=10+10)
DecodeStream_Sonic/single-16     273µs ± 7%     191µs ± 4%  -30.03%  (p=0.000 n=9+10)
DecodeStream_Sonic/4x-16        1.49ms ± 2%    0.59ms ± 7%  -59.98%  (p=0.000 n=10+10)
DecodeStream_Sonic/double-16     679µs ± 3%     237µs ± 5%  -65.00%  (p=0.000 n=10+9)
DecodeStream_Sonic/small-16     27.0µs ± 8%     1.6µs ± 3%  -94.17%  (p=0.000 n=10+9)

name                          old alloc/op   new alloc/op   delta
DecodeStream_Sonic/halt-16       265kB ± 0%     142kB ± 1%  -46.38%  (p=0.000 n=10+10)
DecodeStream_Sonic/double-16    1.20MB ± 0%    0.28MB ± 0%  -76.65%  (p=0.000 n=10+10)
DecodeStream_Sonic/4x-16        2.79MB ± 0%    0.56MB ± 0%  -79.87%  (p=0.000 n=10+10)
DecodeStream_Sonic/single-16    1.32MB ± 0%    0.14MB ± 0%  -89.36%  (p=0.000 n=10+9)
DecodeStream_Sonic/small-16      269kB ± 0%       1kB ± 0%  -99.45%  (p=0.000 n=10+10)

name                          old allocs/op  new allocs/op  delta
DecodeStream_Sonic/small-16       21.0 ± 0%      20.0 ± 0%   -4.76%  (p=0.000 n=10+10)
DecodeStream_Sonic/halt-16        12.0 ± 0%       9.0 ± 0%  -25.00%  (p=0.000 n=10+10)
DecodeStream_Sonic/double-16      18.0 ± 0%       9.0 ± 0%  -50.00%  (p=0.000 n=10+10)
DecodeStream_Sonic/4x-16          29.0 ± 0%      14.0 ± 0%  -51.72%  (p=0.000 n=10+10)
DecodeStream_Sonic/single-16      11.0 ± 0%       5.0 ± 0%  -54.55%  (p=0.000 n=10+10)

[codecov-commenter]

Codecov Report

Merging #550 (eb1f9e4) into main (fd7e221) will increase coverage by 0.28%.
Report is 3 commits behind head on main.
The diff coverage is 97.18%.

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@@            Coverage Diff             @@
##             main     #550      +/-   ##
==========================================
+ Coverage   78.30%   78.59%   +0.28%     
==========================================
  Files          69       69              
  Lines       10686    10692       +6     
==========================================
+ Hits         8368     8403      +35     
+ Misses       1955     1924      -31     
- Partials      363      365       +2     

Files	Coverage Δ
internal/decoder/stream.go	92.17% <97.18%> (+28.87%)	⬆️

... and 1 file with indirect coverage changes

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[AsterDY]

fix #378