Deep copy requirements in Gem::Specification and Gem::Requirement

[flavorjones]

What was the end-user or developer problem that led to this PR?

While drafting rake-compiler/rake-compiler#236, I needed to modify the required_rubygems_version of a Gem::Specification that was a copy of the original.

While doing so, I discovered two things:

• modifying the required_rubygems_version of a Gem::Specification copy also mutates the original's
• modifying the requirements of a Gem::Requirements copy also mutates the original's

That is:

requirement2 = requirement.dup

# this modifies original `requirement`
requirement2.concat([">= 3.3.22"])

and

spec2 = spec.dup

# this modifies original `spec`'s `required_rubygems_version`
spec2.required_rubygems_version.concat([">= 3.3.22"])

This was confusing and led to more complex code and tests.

What is your fix for the problem, implemented in this PR?

This PR implements what I believe to be the common-sense behavior of "copy" for these classes to avoid accidental mutation of the originals:

• deep-copies the Gem::Requirement attributes of a Gem::Specification
• deep-copies the @requirements attribute of a Gem::Requirement

With this new behavior, my use case described above can be solved by:

spec2 = spec.dup
spec2.required_rubygems_version.concat([">= 3.3.22"])

Make sure the following tasks are checked

• Describe the problem / feature
• Write tests for features and bug fixes
• Write code to solve the problem
• Make sure you follow the current code style and write meaningful commit messages without tags

[deivid-rodriguez]

Looks good to me. Definitely more common sense! Just left a small comment.

[deivid-rodriguez]

Thanks!