fix(adb/threadpool): remove waitgroups and fix segfault

[0xNineteen]

the main fix is to remove the waitgroups in accounts-db loading/validating so we can have errors propagate correctly. while doing this, i also noticed a bug in the homo-threadpool impl where addOne to existing tasks will cause re-allocs on existing thread state leading to a segfault. there was also some code in repair which would join the threadpool after a single schedule in a loop, which i assumed was a bug and fixed as well.

there was also a bug which tsan found where an allocator was used in the registry without a lock which i fixed as well.

this lead to another bug in tsan about registry init race conditions which was fixed in 553c803.

What changed?

• Refactored spawnThreadTasks to use a homogeneous thread pool instead of raw thread spawning
• Removed single-threaded code paths in favor of unified multi-threaded implementation
• Modified loadFromSnapshot to return void instead of duration
• Adjusted testnet accounts per file estimate from 1000 to 500
• Added thread pool capacity pre-allocation to avoid reallocation during scheduling
• Added new test case for spawnThreadTasks

[0xNineteen]

• fix(adb/threadpool): remove waitgroups and fix segfault #522 👈 (View in Graphite)
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[InKryption]

Two very minor comments, overall a solid improvement and fix.