Improve Script Error Handling and Argument Parsing

[Piyushhhhh]

• Error Handling: Add error checking for each significant command to make debugging easier if something goes wrong.

• Refactor Argument Parsing: Use a while loop with getopts for more robust and readable argument parsing

• Improve Variable Initialization: Set default values for REPEAT directly instead of using conditional logic later.

• Check for Command Existence: Ensure required commands like git and flutter are available.

• Optimize Flutter Installation Check: Check if Flutter is already installed and only clone if necessary.

• Make Path Management More Robust: Ensure the Flutter binary is added to the PATH only if it was cloned.

If you had to change anything in the flutter/tests repo, include a link to the migration guide as per the breaking change policy.

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• [yes ] I read the Tree Hygiene wiki page, which explains my responsibilities.

• [yes ] I read the Flutter Style Guide recently, and have followed its advice.

• [yes ] I signed the CLA.

• [ yes] I updated/added relevant documentation (doc comments with ///).

• [yes ] All existing and new tests are passing.

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[chunhtai]

Closing this as inactive, feel free to reopen once you have time to come back to this pr