chore: remove regex stripping trailing slash from configured url

[jeffsmale90]

📝 Description

When configuring the delegation storage client, a regex is used to strip trailing slashes from the provided URL. This change removes that and replaces it with a bounded mechanism.

🔄 What Changed?

Regex stripping trailing slashes was replaced with mechanism that inserts a separating slash if one doesn't exist on the provided URL.

🚀 Why?

Resolves https://github.com/MetaMask/delegation-toolkit/security/code-scanning/2 polynomial regex expression.

🧪 How to Test?

No changes in behaviour.

Configuring the delegation storage url with a trailing '/' should continue to work.
"accepts an apiUrl with a trailing slash" added to packages/delegation-toolkit/test/experimental/delegationStorage.test.ts validates this case

⚠️ Breaking Changes

• No breaking changes
• Breaking changes (describe below):

📋 Checklist

Check off completed items:

• Code follows the project's coding standards
• Self-review completed
• Documentation updated (if needed)
• Tests added/updated
• Changelog updated (if needed)
• All CI checks pass