Fix #406: Prevent multiple server sessions at startup

[isc-klu]

Problem

When VS Code opens with many tabs, each tab concurrently calls makeRESTRequest(), creating multiple sessions to the same server.

Solution

Serialize REST requests per server using promise-based queueing:

• First request authenticates and stores session cookie
• Concurrent requests wait and reuse the session cookie
• Subsequent requests use cached cookies immediately

Changes

• Changed cookiesCache to store promises instead of raw cookie arrays
• Made getCookies()/updateCookies() async with queue logic
• Added updateCookies() in catch block to ensure promises always resolve

[isc-bsaviano]

Sorry for nor reviewing this sooner KC. I think a more simple solution is to create sessions for all current workspace folders on activation. If we do it before activation completes then we know that all intellisense requests will be using cookies since those requests won't be sent until after activation. We can add a code block here that is similar to the the one from the main extension. The we won't need to modify any other code.

[isc-klu]

Sorry for nor reviewing this sooner KC. I think a more simple solution is to create sessions for all current workspace folders on activation. If we do it before activation completes then we know that all intellisense requests will be using cookies since those requests won't be sent until after activation. We can add a code block here that is similar to the the one from the main extension. The we won't need to modify any other code.

Thanks for the guidance. Please check the latest diff.