fix(rules): preserve equals signs in query parameter values

[jashkarangiya]

Closes #121

📜 Summary of changes:

Query parameter parsing previously split on every equals sign and kept only the first part of the value. That changed token=abc== into token=abc whenever a rule rebuilt the URL.

This updates the parser to split on the first equals sign and preserve the rest of the value. Key-only parameters such as ?debug are also kept as key-only parameters.

Regression coverage checks both paths that exposed the bug:

• adding a parameter while an existing value contains equals signs
• removing an unrelated parameter while preserving that value

🎥 Demo Video:

Video/Demo: Not applicable. This is a parser-only fix with no UI change.

✅ Checklist:

• Make sure linting and unit tests pass.
• No install/build warnings introduced.
• Verified UI in browser.
• For UI changes, added/updated analytics events (if applicable).
• For changes in extension's code, manually tested in Chrome and Firefox.
• Added/updated unit tests for this change.
• Raised pull request to update corresponding documentation (if already exists).
• Added demo video showing the changes in action (if applicable).

🧪 Test instructions:

The production rule-processor build passes with npm run build from common/rule-processor.

Direct checks against the generated bundle pass for:

1. Adding added=2 to https://example.com?token=abc==&remove=1.
2. Removing remove from the same URL.
3. Removing an unrelated parameter while preserving a key-only parameter.

The full Karma suite is not marked as passing. It fails in the same way on untouched upstream master because of the existing shared-constants initialization problem.

🔗 Other references:

• Bug report: [Bug] Query parameter rules drop equals signs from existing values #121

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