feat: improve syntax parser for pattern

[cyriltovena]

What this PR does / why we need it:

Thought we had an issue there, but not really, although we still useful to get 35% less alloc.

❯ benchstat before.txt after.txt
name          old time/op    new time/op    delta
ParseExpr-16    8.73µs ± 3%    7.79µs ± 1%  -10.81%  (p=0.008 n=5+5)

name          old alloc/op   new alloc/op   delta
ParseExpr-16    5.07kB ± 0%    3.28kB ± 0%  -35.27%  (p=0.008 n=5+5)

name          old allocs/op  new allocs/op  delta
ParseExpr-16      26.0 ± 0%      25.0 ± 0%   -3.85%  (p=0.008 n=5+5)

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
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[cyriltovena]

Let's merge after 3.0 don't think it will make a big difference for the release.