fix: Use fill-opacity and stroke-opacity for hex colors with alpha

[DenverCoder1]

Description

Adds support for hex colors in the format #rgba / #rrggbbaa where aa is the opacity (00-FF) when converting to PNG.

Inkscape does not currently support the #rgba / #rrggbbaa syntax - see https://gitlab.com/inkscape/inbox/-/issues/8215

Other SVG renderers may also have issues with certain colors fixed.

Type of change

• Bug fix (added a non-breaking change which fixes an issue)
• New feature (added a non-breaking change which adds functionality)
• Updated documentation (updated the readme, templates, or other repo files)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

• Tested locally with a valid username
• Tested locally with an invalid username
• Ran tests with composer test
• Added or updated test cases to test new features

Checklist:

• I have checked to make sure no other pull requests are open for this issue
• The code is properly formatted and is consistent with the existing code style
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

Screenshots