feat: add RemoveTag engine method

[jaime-amate]

The aim of this PR is to add a function that allows to remove a defined tag. This is useful for my specific need as I need to disable a standard tag ({% include %}) and still get a parse error.

Currently in order to disable a standard tag, you can:

// Register a tag that always returns an error
engine.RegisterTag("include", func(c render.Context) (string, error) {
    return "", fmt.Errorf("Tag include is not allowed")
})

This overrides the existing tag functionaly of include and will throw an error at render time. Adding RemoveTag allows to remove standard tags dinamically.

Checklist

• I have read the contribution guidelines.
• make test passes.
• make lint passes.
• New and changed code is covered by tests.
• Performance improvements include benchmarks.
• Changes match the documented (not just the implemented) behavior of Shopify.

[Copilot]

Pull request overview

This PR adds a RemoveTag method to the Engine API, enabling dynamic removal of tag definitions from the engine configuration. This addresses the use case of disabling standard tags (like {% include %}) and getting parse-time errors instead of render-time errors when those tags are used.

Key changes:

• Added RemoveTag method to render.Config that uses Go's delete function to remove tags from the internal map
• Exposed RemoveTag through the public Engine API with comprehensive documentation
• Added test coverage verifying that removed tags cause parse/render errors

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
render/tags.go	Implements low-level RemoveTag method on Config that deletes tag from internal map
engine.go	Exposes public RemoveTag API with clear documentation about idempotent behavior
engine_examples_test.go	Adds test verifying custom tag removal causes errors on subsequent use

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[Copilot]

The test only verifies removing a custom tag (echo), but the PR description specifically mentions removing standard tags like {% include %} to get parse errors. Consider adding a test case that removes a standard tag to ensure this use case works as intended.

Example:

t.Run("RemoveStandardTag", func(t *testing.T) {
    engine := NewEngine()
    source := `{% if true %}test{% endif %}`
    
    _, err := engine.ParseAndRenderString(source, emptyBindings)
    require.NoError(t, err)
    
    engine.RemoveTag("if")
    
    _, err = engine.ParseAndRenderString(source, emptyBindings)
    require.Error(t, err)
})

[osteele]

Consider whether this should be RemoveTag or UnregisterTag. The first reads better in isolation; the second has better symmetry with RegisterTag.

This is just a question for you, not a requirement for me to accept the PR. I'm okay with either. Don't do both though! This ends up making it harder to work with client code.

[osteele]

As a test, this should go in engine_test.go. Or rename it to ExampleEngine_RemoveTag as a testable example.

[osteele]

Thank you for contribution! This looks solid. A couple of minor review comments are attached.