feat: improve string encoding

[tdakkota]

Benchstat result:

name                           old time/op    new time/op    delta
EncoderBigObject-12              7.56µs ± 2%    4.01µs ± 1%  -46.97%  (p=0.000 n=10+10)
Encoder_Field/1/Manual-12        20.6ns ± 2%    18.6ns ± 0%   -9.83%  (p=0.000 n=10+9)
Encoder_Field/1/Callback-12      26.2ns ± 5%    24.8ns ± 5%   -5.20%  (p=0.034 n=10+10)
Encoder_Field/5/Manual-12        84.3ns ± 1%    81.9ns ± 0%   -2.89%  (p=0.000 n=10+9)
Encoder_Field/5/Callback-12       112ns ± 4%     126ns ± 1%  +12.43%  (p=0.000 n=10+10)
Encoder_Field/10/Manual-12        173ns ± 1%     150ns ± 0%  -13.15%  (p=0.000 n=10+9)
Encoder_Field/10/Callback-12      200ns ± 2%     182ns ± 1%   -9.30%  (p=0.000 n=9+10)
Encoder_Field/100/Manual-12      1.62µs ± 1%    1.39µs ± 0%  -13.91%  (p=0.000 n=10+9)
Encoder_Field/100/Callback-12    1.86µs ± 1%    1.65µs ± 0%  -11.15%  (p=0.000 n=10+10)

name                           old speed      new speed      delta
EncoderBigObject-12             674MB/s ± 2%  1271MB/s ± 1%  +88.57%  (p=0.000 n=10+10)

[codecov]

Codecov Report

Merging #9 (155802f) into main (d76a769) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main        #9   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           23        23           
  Lines         1871      1872    +1     
=========================================
+ Hits          1871      1872    +1     

Impacted Files	Coverage Δ
enc_str.go	100.00% <100.00%> (ø)

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[ernado]

name                           old time/op    new time/op    delta
EncoderBigObject-32              5.89µs ± 2%    3.51µs ± 2%  -40.43%  (p=0.000 n=9+9)
Encoder_Field/1/Manual-32        16.0ns ± 2%    16.8ns ± 3%   +4.63%  (p=0.000 n=9+9)
Encoder_Field/1/Callback-32      21.0ns ± 3%    20.9ns ± 5%     ~     (p=0.593 n=10+10)
Encoder_Field/5/Manual-32        68.9ns ± 2%    65.3ns ± 2%   -5.32%  (p=0.000 n=10+10)
Encoder_Field/5/Callback-32      79.2ns ± 4%    78.5ns ± 1%     ~     (p=0.633 n=10+8)
Encoder_Field/10/Manual-32        143ns ± 2%     133ns ± 4%   -6.92%  (p=0.000 n=10+10)
Encoder_Field/10/Callback-32      162ns ± 4%     157ns ± 2%   -3.18%  (p=0.001 n=9+9)
Encoder_Field/100/Manual-32      1.33µs ± 2%    1.22µs ± 3%   -7.89%  (p=0.000 n=10+10)
Encoder_Field/100/Callback-32    1.49µs ± 5%    1.44µs ± 3%   -3.24%  (p=0.005 n=10+10)

name                           old speed      new speed      delta
EncoderBigObject-32             864MB/s ± 2%  1451MB/s ± 2%  +67.87%  (p=0.000 n=9+9)

name            old time/op    new time/op    delta
OTEL_Encode-32     596ns ±12%     390ns ± 3%  -34.56%  (p=0.008 n=5+5)

name            old speed      new speed      delta
OTEL_Encode-32   716MB/s ±12%  1087MB/s ± 3%  +51.75%  (p=0.008 n=5+5)