rubocop: reduce every regex evaluation for performance

[kenhys]

Which issue(s) this PR fixes:
Fixes #

What this PR does / why we need it:

This is cosmetic change, it does not change behavior at all. The following rubocop configuration detects it.

Performance/ConstantRegexp:
  Enable: true

Benchmark result:

ruby 3.2.8 (2025-03-26 revision 13f495dc2c) +YJIT [x86_64-linux]
Warming up --------------------------------------
 interpret everytime    26.127k i/100ms
      interpret once     3.172M i/100ms
Calculating -------------------------------------
 interpret everytime    254.171k (± 2.6%) i/s    (3.93 μs/i) -      1.280M in   5.040357s
      interpret once     33.755M (± 1.7%) i/s   (29.62 ns/i) -    171.289M in   5.075867s

Comparison:
      interpret once: 33755320.3 i/s
 interpret everytime:   254171.5 i/s - 132.81x  slower

Regex should not be evaluated every time, use /o to evaluate only once because it expands constant in /#{...}/ expression.

Appendix: benchmark script

require 'bundler/inline'
gemfile do
  source 'https://rubygems.org'
  gem 'benchmark-ips'
  gem 'benchmark-memory'
end

Benchmark.ips do |x|
  ZERO_OR_MORE_SPACING = /(?:[ \t\r\n]|\z|\#.*?(?:\z|[\r\n]))*/
  x.report("interpret everytime") {
    /(?:#{ZERO_OR_MORE_SPACING}\>)/
  }
  x.report("interpret once") {
    /(?:#{ZERO_OR_MORE_SPACING}\>)/o
  }
  x.compare!
end

Docs Changes:

N/A

Release Note:

N/A

[daipom]

Thanks!