fix: add base64 gem dependency for Ruby 3.3+ compatibility

[wasim-builds]

Summary

Adds the base64 gem as an explicit dependency in liquid.gemspec.

Problem

The base64 gem was loaded from the standard library in Ruby 3.3, producing this deprecation warning:

warning: base64 was loaded from the standard library, but will no longer be part of the default gems since Ruby 3.4.0. Add base64 to your Gemfile or gemspec.

Starting with Ruby 3.4, the base64 gem is no longer part of the default gems, meaning require 'base64' will raise a LoadError unless the gem is explicitly depended on.

This is the second half of the fix for #1772 -- the bigdecimal dependency was already added previously.

Changes

• liquid.gemspec: Added s.add_dependency("base64")

Testing

This is a gemspec-level dependency declaration change. No code logic is modified, so existing tests continue to pass. The fix ensures that require 'base64' in lib/liquid/standardfilters.rb works without deprecation warnings on Ruby 3.3+ and without errors on Ruby 3.4+.

[wasim-builds]

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[wasim-builds]

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