Motivation / Background

This Pull Request has been created because I want to make these methods faster, because they're extremely common in the database seeds/tests of every Rails app I've ever worked on.

The changes in this PR were generated using Claude Code w/ Fable 5. They have been reviewed and tested by me for correctness.

• username: pick the username shape (first-name-only vs first+last) before generating names, so the discarded variant is never built.
• password: reuse frozen digit/special-char tables and grow the character bag in place with concat instead of += (which copies the whole array each time).
• base64: reuse frozen urlsafe/standard character tables and append into a pre-sized String instead of building an intermediate array.
• sanitize_email_local_part: replace invalid characters with a single gsub against a character-class regex instead of rebuilding the allowed-character array and scanning it per character.

Additional information

Benchmark (Ruby 3.4.9, arm64-darwin25, benchmark-ips):

require 'benchmark/ips'
require 'faker'

Benchmark.ips do |x|
  x.config(warmup: 1, time: 2)
  x.report('username') { Faker::Internet.username }
  x.report('email') { Faker::Internet.email }
  x.report('password') { Faker::Internet.password }
  x.report('base64') { Faker::Internet.base64 }
end

Results:

main:        username   41.048k (+/-14.7%) i/s
             email      21.683k (+/- 0.7%) i/s
             password  394.792k (+/- 4.8%) i/s
             base64    183.509k (+/- 2.4%) i/s
this commit: username   79.313k (+/-18.2%) i/s  (~1.9x)
             email      37.246k (+/- 1.3%) i/s  (~1.7x)
             password  451.683k (+/- 1.0%) i/s  (~1.14x)
             base64    462.621k (+/- 0.5%) i/s  (~2.5x)

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug, refactor something, or add a feature.
• Tests and Rubocop are passing before submitting your proposed changes.

If you're proposing a new generator or locale:

• Double-check the existing generators documentation to make sure the new generator you want to add doesn't already exist.
• You've reviewed and followed the Contributing guidelines.