Make JS engines optional dependencies when pulling in gost-dom/browser

[tomlinford]

Right now pulling in gost-dom/browser also adds v8 engine as a dependency, which is pretty heavy. This change lets API consumer pick which JS engine to use, if any.

[coderabbitai]

Walkthrough

This pull request restructures JavaScript engine dependencies by moving them from the main module into separate optional sub-modules. The main go.mod removes direct dependencies on v8go and Sobek, while new go.mod files are introduced for scripting/v8engine, scripting/sobekengine, and v8browser that declare these dependencies independently. Documentation is expanded to describe the available engine options and usage instructions. The internal/test/wpt module adds a v8engine dependency. This change isolates heavy engine-specific dependencies into optional packages.

Possibly related PRs

• change mentions of goja to sobek #180: Renames Goja to Sobek and adjusts v8engine/sobekengine module paths and package names alongside this restructuring
• Test/updates #166: Refactors tests to be engine-agnostic and removes v8engine-specific test coverage as engines become optional modules
• Fix/remove v8go deps #183: Removes v8go usage and V8-specific code paths from the main codebase, complementing the dependency extraction into separate modules

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: making JavaScript engines optional dependencies instead of default/required ones in the gost-dom/browser package.
Description check	✅ Passed	The description clearly explains the motivation and purpose: avoiding heavy v8 engine dependencies by default while allowing consumers to choose their preferred JS engine or none.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[coderabbitai]

Actionable comments posted: 1

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

README_SCRIPT_ENGINE.md (1)

114-114: Fix typo in link reference.

The link reference should be [Sobek] not [Sobak] to match the project name.

Proposed fix

-[Sobak]: https://github.com/grafana/sobek
+[Sobek]: https://github.com/grafana/sobek

[coderabbitai]

⚠️ Potential issue | 🟡 Minor

Fix trailing space.

Proposed fix

-- `github.com/gost-dom/browser/scripting/sobekengine` - Pure Go JavaScript engine 
+- `github.com/gost-dom/browser/scripting/sobekengine` - Pure Go JavaScript engine

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

	- `github.com/gost-dom/browser/scripting/sobekengine` - Pure Go JavaScript engine
	- `github.com/gost-dom/browser/scripting/sobekengine` - Pure Go JavaScript engine

🧰 Tools

🪛 markdownlint-cli2 (0.18.1)

71-71: Trailing spaces
Expected: 0 or 2; Actual: 1

(MD009, no-trailing-spaces)