ANSI parser speedup

[DrJosh9000]

Description

Significant speed savings:

❯ benchstat ansi-parser-{maps,arrays}.txt
goos: darwin
goarch: arm64
pkg: github.com/buildkite/agent/v3/process
cpu: Apple M1 Max
              │ ansi-parser-maps.txt │       ansi-parser-arrays.txt        │
              │        sec/op        │   sec/op     vs base                │
ANSIParser-10           2322.3µ ± 0%   565.3µ ± 1%  -75.66% (p=0.000 n=30)

Context

The secret redactor was sped up a bit by switching away from a map, and I remembered this used maps too.

Changes

• Add a benchmark
• Rename feed to Write in case we want to e.g. io.Copy or MultiWriter into it
• Use [256]*ansiParserState instead of map[byte]ansiParserState

Testing

• Tests have run locally (with go test ./...). Buildkite employees may check this if the pipeline has run automatically.
• Code is formatted (with go fmt ./...)

[pda]

Nice!