Remove Test::More dependency in favor of Test2::API

[yuu-no]

Summary

This PR removes the runtime dependency on Test::More, making Test::Snapshot compatible with Test2::V0 directly.

Changes

• Replace require Test::More with pure Test2::API usage
• Use $ctx->pass/fail/diag instead of Test::More::pass/fail/diag
• Remove $Test::Builder::Level manipulation (no longer needed with context)
• Capture subtest names via test2_add_callback_pre_subtest and Hub metadata
• Refactor _get_filename() to use $0 and Hub metadata instead of Test::Builder metadata

Motivation

Users who prefer Test2::V0 over Test::More can now use Test::Snapshot without pulling in Test::More as a runtime dependency. This also simplifies the codebase by using the modern Test2::API directly.

Test plan

• Existing tests pass (prove -lr t/)
• Added t/snapshot-test2.t for Test2::V0 compatibility testing
• Renamed t/snapshot.t → t/snapshot-testmore.t to clarify test coverage

[yuu-no]

Hi @mohawk2,

I’m just following up on this PR. I believe this change would be beneficial for the project. Could you please take a look when you have a moment?

Thanks!

[mohawk2]

Thank you for the contribution! I've just added GHA CI on this, and rebased your branch over it. You can see above that it's failed the release tests (prove -l xt would have shown this) because you didn't update the MANIFEST. I'll fix that now.

[mohawk2]

I've also removed the blank lines you added (my personal taste) and the return statement at the end of a function, which I gather actually slightly slows the interpreter down.

[mohawk2]

Thank you again! I'll add a note in Changes crediting you, and update the docs.

By the way, you PR-ed this from your master branch, it's considered best practice to do that from a feature branch in your repo instead.