Make PTO duration usage and calculation uniform

We have a few `p.recovery.pto * 3` calculations scattered throughout the codebase. These seem to be used for calculating timeouts. It would be nice to have this logic extracted into its own function.

Examples:
- https://github.com/cloudflare/quiche/blob/83f919f0dcf49f973f8f425a4dcd5754fc47fe33/quiche/src/lib.rs#L8452-L8455
- https://github.com/cloudflare/quiche/blob/83f919f0dcf49f973f8f425a4dcd5754fc47fe33/quiche/src/lib.rs#L3233
- https://github.com/cloudflare/quiche/blob/83f919f0dcf49f973f8f425a4dcd5754fc47fe33/quiche/src/lib.rs#L4706

Start in quiche/src/lib.rs at the three referenced locations and inspect how p.recovery.pto * 3 is used for timeouts. Locate all equivalent calculations, extract the shared logic into a function, and replace the scattered uses. Done means timeout calculations use the common function consistently.

Written by the indexing model from the issue text.