R1:bd4d9d88f2df

Limit remarkup URI protocol length to 32 characters to avoid expensive regex behavior

Summary:
Ref T13608. When searching for bare URIs in remarkup text, don't look for URIs with a protocol string longer than 32 characters.

This avoids a case where the regexp engine may be tricked into executing at `O(N^2)` or some similar complexity.

Test Plan:
- Applied remarkup to "AAAA..." (512KB).
- Before: 64 seconds to process.
- After: <10ms to process.
- Ran unit tests.

Maniphest Tasks: T13608…