Add docs for how to run the full contract test suite locally

[Chucks1093]

Summary
The steps to run the full contract test suite locally are not documented in one place. New contributors spend time discovering the correct commands and environment requirements by reading CI config rather than a clear guide.

Scope

• document the prerequisites needed to run the full contract test suite locally
• list the exact commands to run unit tests, integration tests, and linting
• note any environment variables or local config required before running

Acceptance Criteria

• a new contributor can follow the guide to run the full test suite without external help
• prerequisite tools and versions are listed
• no code changes are required; this is a docs-only issue

Contributor coordination: if you pick this up, reach out in Telegram for updates or clarification: https://t.me/accesslayerorg

[Chigybillionz]

@Chigybillionz has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I can fix this task please

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[khanavi272-spec]

@khanavi272-spec has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @khanavi272-spec to this issue.

[drips-wave]

Congratulations, @khanavi272-spec! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

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