Improve handling of paths with invalid Windows characters

[Saidbek]

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

Fixes #7681

Windows doesn't allow certain characters in filenames (e.g., colons) that are valid on Unix. When gems contain files with these characters, installation fails on Windows with cryptic Errno::EINVAL errors.

This PR adds validation and directs users to report issues to gem authors instead.

• Add InvalidFileNameError with user-friendly messages
• Validate filenames during gem extraction on Windows
• Warn developers when building gems with invalid filenames

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

[larskanis]

This LGTM now, ready to be merged. I tested Windows gem install:

$ gem inst crono:2.0.1
ERROR:  While executing gem ... (Gem::Package::InvalidWindowsFileNameError)
    The gem contains a file 'spec/internal/:memory' with characters in its name that are not allowed on Windows. This is a problem with the 'crono-2.0.1' gem, not Rubygems. Please report this issue to the gem author. (Gem::Package::InvalidWindowsFileNameError)
        C:/Ruby40-arm/lib/ruby/site_ruby/4.0.0/rubygems/package.rb:446:in 'block (2 levels) in Gem::Package#extract_tar_gz'
[...]
       C:/Ruby40-arm/bin/gem:12:in '<main>'

Linux gem install:

$ gem inst crono:2.0.1
Successfully installed crono-2.0.1
Parsing documentation for crono-2.0.1
Done installing documentation for crono after 0 seconds
1 gem installed

Linux gem build:

$ gem build crono.gemspec
WARNING:  make sure you specify the oldest ruby version constraint (like ">= 3.0") that you want your gem to support by setting the `required_ruby_version` gemspec attribute
WARNING:  See https://guides.rubygems.org/specification-reference/ for help
Enter PEM pass phrase:
WARNING:  filename 'spec/internal/:memory' contains characters that are invalid on Windows (e.g., colons). This gem may fail to install on Windows.
  Successfully built RubyGem
  Name: crono
  Version: 2.0.1
  File: crono-2.0.1.gem

And I did run the tests on Windows and Linux. All looks good now.