Add version components digits configuration to DerivedBuildCodeFormatter

[iangmaia]

What does it do?

This PR adds to the DerivedBuildCodeFormatter class the possibility to configure a variable number of digits per version components, so that we have more flexibility to increase the maximum number of builds per a specific major / minor version, for example.

Checklist before requesting a review

• Run bundle exec rubocop to test for code style violations and recommendations.
• Add Unit Tests (aka specs/*_spec.rb) if applicable.
• Run bundle exec rspec to run the whole test suite and ensure all your tests pass.
• Make sure you added an entry in the CHANGELOG.md file to describe your changes under the appropriate existing ### subsection of the existing ## Trunk section.
• If applicable, add an entry in the MIGRATION.md file to describe how the changes will affect the migration from the previous major version and what the clients will need to change and consider.

[AliSoftware]

Mostly 💄 nitpicks + some suggestions to improve the unit tests. Otherwise LGTM 👍

[iangmaia]

@AliSoftware I believe I addressed all the test suggestions!

[AliSoftware]

Just nitpicks to fix code comments, otherwise LGTM so approving to unblock you

[AliSoftware]

👍 Today I re-learned that nil.to_s returns the '' empty string (as opposed to crashing).

This is why even if now you call validate_prefix! from the def initialize without doing the prefix ||= '' anymore first, this prefix_str = prefix.to_s still doesn't crash 👍

[AliSoftware]

💭 I'm surprised that rubocop doesn't complain about you using a local variable here instead of using RSpec's let(:all_digit_combinations) { … } syntax (which I believed was more idiomatic to Rspec)…

I don't mind either approach in practice (should do the same in the end, maybe except some memoizing of the value when using let?). I just wouldn't want a rubocop warning to appear because of this?

[iangmaia]

Yeah I did it first with a let, but had to re-learn that it won't work if we use it as part of the context:

  `all_digit_combinations` is not available on an example group (e.g. a `describe` or `context` block). It is only available from within individual examples (e.g. `it` blocks) or from constructs that run in the scope of an example (e.g. `before`, `let`, etc).