Fixed ReplaceStep to perform a real tree replace

[HassanAkbar]

Metanorma PR checklist

• Breaking changes (list related PRs)
• Documentation update required (create task for this)
• External dependency introduced (documentation update need)
• Gem with native library introduced

Related to lutaml/lutaml-model#720
This PR fixes failures in https://github.com/lutaml/lutaml-model/actions/runs/29395937178/job/87293331371?pr=720

[Copilot]

Pull request overview

This PR updates Prosereflect’s transform pipeline so ReplaceStep performs a true tree-structured replace (rather than rebuilding via fragments), and ensures transformed documents remain traversable with correctly-typed node content.

Changes:

• Implemented Node#replace and switched ReplaceStep#apply to use it, rejecting unsupported slice open boundaries and fixing invert to return a Slice.
• Updated multiple transform steps to rebuild documents via Node#copy so doc.content contains nodes (not a wrapped Fragment).
• Added leaf? / inline? node semantics and extensive specs covering replace edge cases (leaf handling, text merging, boundary insertion behavior).

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
spec/prosereflect/transform/step_content_spec.rb	Adds regression coverage ensuring step results produce traversable documents with node content.
spec/prosereflect/transform/replace_spec.rb	Expands ReplaceStep specs to validate correct text outcomes, node_size stability, and leaf/boundary behaviors.
lib/prosereflect/transform/replace_step.rb	Switches ReplaceStep to delegate to doc.replace, adds open-boundary rejection, and wraps inversion content in a Slice.
lib/prosereflect/transform/replace_around_step.rb	Uses doc.copy to rebuild docs without fragment-wrapping issues.
lib/prosereflect/transform/mark_step.rb	Uses doc.copy when applying/removing marks to preserve correct node content.
lib/prosereflect/transform/attr_step.rb	Uses doc.copy when applying attrs to preserve correct node content.
lib/prosereflect/node.rb	Adds leaf?, inline?, and the core replace implementation used by ReplaceStep.
lib/prosereflect/text.rb	Marks Text as inline to support boundary resolution decisions.
lib/prosereflect/hard_break.rb	Declares hard_break as an inline leaf for correct replace insertion semantics.
lib/prosereflect/image.rb	Declares image as an inline leaf for correct replace insertion semantics.
lib/prosereflect/horizontal_rule.rb	Declares horizontal_rule as a leaf for correct replace insertion semantics.
lib/prosereflect/user.rb	Declares user mention as an inline leaf for correct replace insertion semantics.

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[Copilot]

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.