chore: Fix Typos Across FlutterFire Repository

[gbolahan146]

Description

This PR corrects various typographical errors across the FlutterFire repository, including documentation, comments, and error messages. No functional changes were made—only textual corrections to improve clarity and maintainability.

Changes

Fixed typos in README files, inline comments, and DartDoc comments.

Standardised terminology and grammar for better consistency.

Ensured that all changes do not alter the functionality of any APIs.

Motivation

Clear and professional documentation improves developer experience and reduces ambiguity. These changes contribute to better readability and maintainability of the codebase.

Testing

No tests were added or modified, as this PR does not affect functionality.

Ran dart analyze to confirm no unintended issues were introduced.

Related Issues

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]).
This will ensure a smooth and quick review process. Updating the pubspec.yaml and changelogs is not required.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (melos run analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change.
• No, this is not a breaking change.