Fix/email validation regex

[cubegao]

Fix the email validation function by correcting the regex escape pattern.

The previous implementation used an escaped $ in a raw string, which caused the regex to match a literal $ character instead of the end-of-string anchor.

Update the regex pattern to properly validate email formats.

Description

This PR fixes an issue in the email validation function where the regular expression pattern did not correctly handle the end-of-string anchor.

The previous implementation incorrectly escaped the $ character inside a Dart raw string. As a result, the regex engine treated it as a literal character instead of the end-of-string matcher, causing valid email addresses to fail validation.

This change updates the regex pattern to use the correct $ anchor and ensures email validation behaves as expected.

Related Issues

N/A

Testing

• Verified that valid email addresses are correctly accepted.
• Verified that invalid email formats are rejected.

Pre-launch Checklist

• The code changes have been tested.
• The updated validation logic works as expected.
• Documentation updates are not required.

[gemini-code-assist]

Code Review

This pull request corrects a bug in the email validation regular expression within EmailFunction by fixing an incorrectly escaped end anchor, and introduces comprehensive unit tests to verify its behavior. The reviewer recommends optimizing performance by declaring the RegExp as a static final field to prevent recompiling it on every function invocation.

[gemini-code-assist]

Instantiating a RegExp on every invocation of executeSync is inefficient because compiling a regular expression is a relatively expensive operation. Since EmailFunction has a const constructor, you cannot declare a non-static instance field. Instead, consider declaring the RegExp as a static final field inside the EmailFunction class (or as a private top-level variable in the file) to compile it only once.