[variant] Handle CV types as arguments

[Yaraslaut]

Closes #19

Will make it a draft since requires rebase on top of #18

[Copilot]

Pull Request Overview

This PR enhances the variant implementation to handle CV-qualified types as arguments to variant operations. The primary goal is to allow the variant to work correctly with const/volatile qualified types in both storage and access operations.

Key Changes

• Enhanced variant template argument handling to support CV-qualified types
• Added comprehensive test coverage for CV-qualified variants and reference-based get operations
• Improved type deduction for variant assignment operations

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
include/rsl/variant	Core variant implementation updates for CV type handling, assignment operators, and storage generation
test/variant/variant.get/get.cpp	Comprehensive test implementation for variant get operations with CV-qualified types
test/variant/variant.assign/assign.cpp	New test file for variant assignment operations
test/variant/variant.ctor/default.cpp	Additional constructor tests for CV-qualified variants
Multiple CMakeLists.txt	Build configuration updates to include new test files

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[Tsche]

other than that lgtm

[Tsche]

do not spell out std::meta:: here. remove_cv can be found via ADL - the argument is of type std::meta::info. Please apply this change to tagged_variant::make_storage as well.

[Tsche]

Also I can't help but wonder if remove_cvref is better here. Union members cannot be references - so variant<T&> is rejected either way. Might be worth it to make extra sure it cannot possibly fail at this point.