[pgAdmin] Startup speed improvements + identified bottlenecks (related to issue #9770)

Hi,

I have been looking into *pgAdmin desktop startup performance and
identified multiple bottlenecks in the startup path. *A quick summary:

- Synchronous DB migrations blocking startup
- Redundant table validation on every launch
- Eager loading of all modules/blueprints
- Driver/auth registries loaded upfront
- 1s polling delay in backend readiness detection
- Sync logging during startup

As a first step, I have implemented a small fix for the polling issue
(adaptive polling instead of fixed 1000ms), which improves responsiveness
without touching backend logic. *Also, the startup feels noticeably
slower *than
expected due to the amount of synchronous work being done upfront, which is
what led me to dig into this.

*Before opening a PR *for this change, I wanted to check if this approach
is acceptable.

This is *part of ongoing work around issue #9770
<https://github.com/pgadmin-org/pgadmin4/issues/9770>, *and I plan to
address the other bottlenecks incrementally.

Thanks and regards
Hari