Refactor cms-loader to use async/await for clarity

[raisakshii]

Description

Refactors the readIgArchive method in CMSLoader to use modern asynchronous patterns (async/await and Promise.all). This resolves a potential race condition during file parsing and significantly improves code readability.

Key Changes

• Fixed Race Condition: Replaced the fragile manual counter (let i = 1) with Promise.all to guarantee all files are completely unzipped and parsed before triggering the onFileRead callback.
• Modernized Syntax: Migrated from nested .then() chains to a flat async/await control flow, eliminating callback hell.
• Safer Error Handling: Added a try/catch block around the archive parsing logic to ensure the loadingManager resolves gracefully even if the .ig file is corrupt.
• Optimized string replacements using a single-pass regex and added a finally block for reliable loading manager resolution.

[raisakshii]

could you please review this PR when you get a chance?

[lavjeetrai]

AFAIU the approach is good ,but fix that failing error first

[raisakshii]

thanks for review.i have converted it into draft .i'll reopen it when i 'll fix the errors

[raisakshii]

@EdwardMoyse , could you please review this PR when you have time.