Fix runtime safety and state consistency issues

[HeresHavi]

Summary

Fixed nine runtime safety and persistence issues across the client, server, and shared task scheduler.

The changes cover:

• Input and packet validation for resource paths, resource-start names, join data, server queries, and no-cache scripts.
• Safe shutdown and background server-cache saving.
• Backup finalization and retrying failed account saves.

Each fix is kept in a focused commit for easier review.

Motivation

These problems mostly appeared during shutdown, malformed input, temporary database failures, filesystem errors, or background cache updates. Normal behavior could appear fine while the failure path dropped work, accepted the wrong response, or left saved data in an inconsistent state.

For example, a temporary database lock could cause an account update to be lost instead of retried. A failed backup rename could also be treated as success and allow older working backups to be removed.

Test plan

Runtime

• Connection: Started an isolated x64 server with 206 resources, then connected, disconnected, reconnected, and shut it down normally.
• Join Data: Confirmed the deprecated compatibility field contained exactly 32 zero bytes before a successful join.
• Resource Paths: Rejected empty and incomplete paths on both the client and server while a valid file path still worked.
• Resource Names: Confirmed a 255-byte exported function name worked and a 256-byte name was rejected without breaking the connection.
• Script Packets: Confirmed a normal no-cache script transferred and executed. Truncated, zero, oversized, and mismatched lengths were rejected.
• Server Browser: Sent a response from the wrong port before the correct response and confirmed only the requested endpoint was accepted.
• Server Cache: Saved and reloaded 3,491 entries without invalid or duplicate endpoints.
• Backups: Confirmed a successful backup opened normally. Forced a rename failure and confirmed older backups were preserved.
• Accounts: Forced an asynchronous save to fail with database is locked, then confirmed it retried automatically and persisted the updated password.

Builds and Tests

• Debug | Win32: Clean client and server component builds passed, 305 client tests passed.
• Release | Win32: Clean client and server component builds passed, 305 client tests passed.
• Debug | x64: Server build passed.
• Release | x64: Server build passed.
• Scheduler shutdown test passed 1,000 consecutive runs in both Debug and Release.
• Ran clang-format.

Checklist

• Your code should follow the coding guidelines.
• Smaller pull requests are easier to review. If your pull request is beefy, your pull request should be reviewable commit-by-commit.