Enable Frozen String Literal in production code

[tagliala]

Close #780

[tagliala]

I'm a little bit surprised about

      def fetch_manual_template(view_path, file)
        Dir[File.join("{#{view_path.join(",")}}", "{#{file},#{partialized(file)}}" + ".{*.,}rabl")].first
      end

Wasn't expecting this to pass on Ruby < 3.0 🤔

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No, this is not surprising at all. string_a + string_b creates a new object

[Copilot]

Pull request overview

This pull request enables frozen string literals in all production code files by adding the # frozen_string_literal: true magic comment at the top of each Ruby file in the lib/ directory. This is a best practice in modern Ruby that improves performance and memory usage by preventing string literals from being modified.

Changes:

• Added # frozen_string_literal: true comment to all 18 Ruby files in the lib/ directory
• Removed redundant .freeze call on a string literal in lib/rabl/helpers.rb (line 133)
• Updated CHANGELOG.md to document the frozen string literal support

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lib/rabl.rb	Added frozen string literal pragma
lib/rabl/builder.rb	Added frozen string literal pragma
lib/rabl/cache_engine.rb	Added frozen string literal pragma
lib/rabl/configuration.rb	Added frozen string literal pragma
lib/rabl/digestor.rb	Added frozen string literal pragma
lib/rabl/digestor/rails3.rb	Added frozen string literal pragma
lib/rabl/digestor/rails41.rb	Added frozen string literal pragma
lib/rabl/digestor/rails5.rb	Added frozen string literal pragma
lib/rabl/engine.rb	Added frozen string literal pragma
lib/rabl/helpers.rb	Added frozen string literal pragma and removed redundant .freeze call
lib/rabl/multi_builder.rb	Added frozen string literal pragma
lib/rabl/partials.rb	Added frozen string literal pragma
lib/rabl/railtie.rb	Added frozen string literal pragma
lib/rabl/renderer.rb	Added frozen string literal pragma
lib/rabl/sources.rb	Added frozen string literal pragma
lib/rabl/template.rb	Added frozen string literal pragma
lib/rabl/tracker.rb	Added frozen string literal pragma
lib/rabl/version.rb	Added frozen string literal pragma
CHANGELOG.md	Added entry for version 0.18.0 documenting frozen string literal support

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