[pkg/stanza] improve performance

[newly12]

Description:

The idea is to avoid making []byte every time to improve performance. In fact we had previously done benchmark against v0.52.0 and recently v0.60.0 and noticed the performance regression, give it one CPU and 40 files to be ingested, emitted logs/s reduced from ~254k/s to ~140k/s. most of cpu time is used by decoding and underlying runtime.makeslice, the new implementation is similar to v0.52.0.

Link to tracking Issue:
#16028

Testing:

Documentation:

$ benchstat old.txt new.txt
name                        old time/op  new time/op  delta
FileInput/Single-10         1.30µs ±13%  1.05µs ±10%  -19.45%  (p=0.008 n=5+5)
FileInput/Glob-10           6.32µs ±12%  4.25µs ± 8%  -32.73%  (p=0.008 n=5+5)
FileInput/MultiGlob-10      5.98µs ± 3%  4.17µs ± 9%  -30.29%  (p=0.008 n=5+5)
FileInput/MaxConcurrent-10  5.42µs ± 4%  4.26µs ±15%  -21.54%  (p=0.008 n=5+5)
FileInput/FngrPrntLarge-10  1.21µs ± 1%  1.06µs ±12%  -12.52%  (p=0.008 n=5+5)
FileInput/FngrPrntSmall-10  1.34µs ± 7%  1.00µs ± 6%  -25.32%  (p=0.008 n=5+5)

[djaglowski]

Great find, @newly12. Thanks for the improvement.

[djaglowski]

Thank you @newly12