Create a separate syslog parsing machine per message

[camdencheek]

Description of Changes

Using the syslog parser concurrently was causing issues because the state machine was being reused. This PR makes a new state machine per syslog message.

Please check that the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• Add a changelog entry (for non-trivial bug fixes / features)
• CI passes

[djaglowski]

Log Files	Logs / Second	CPU Average (%)	Memory Average (MB)
1	1000	3.1724944	24.624191
1	5000	5.965741	33.35547
1	10000	10.879499	44.164467
1	50000	40.846073	103.742325
1	100000	71.00953	168.52452
10	100	4.3794312	28.974676
10	500	8.517425	36.725754
10	1000	11.207158	42.550106
10	5000	46.777233	111.32489
10	10000	79.87665	179.13873

[codecov]

Codecov Report

Merging #61 into master will not change coverage.
The diff coverage is 60.00%.

@@           Coverage Diff           @@
##           master      #61   +/-   ##
=======================================
  Coverage   74.94%   74.94%           
=======================================
  Files          63       63           
  Lines        3835     3835           
=======================================
  Hits         2874     2874           
  Misses        718      718           
  Partials      243      243           

Impacted Files	Coverage Δ
operator/builtin/parser/syslog.go	74.31% <60.00%> (ø)

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