sqlx-pool-guard: allocate more memory on windows

[pronebird]

Sentry picked up the following error on Windows:

imp::check_files_closed() failure: The specified information record length does not match the length required for the specified information class. (os error -805306364)

I have concluded that It's possible for the open file handles table to grow between calls to NtQuerySystemInformation resulting in the buffer being too small two times in a row.

In order to alleviate this, we should take a system returned length as a hint and allocate a bit larger buffer to avoid stumbling upon the same error on the next call.

Changes in this PR:

• Allocate 1.5x more memory than reported by the system to provide a safety margin
• Increase number of retry attempts to 5

JIRA-VPN-3688

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This change is