dirstate-v2: Separate Rust structs for Timestamp and PackedTimestamp PackedTimestamp is now exclusively for dirstate-v2 serialization purpose. It contains unaligned big-endian integers. Timestamp is used everywhere else and contains native Rust integers. Differential Revision: https://phab.mercurial-scm.org/D11632

dirstate-v2: Change the representation of negative directory mtime Change it from how I previously thought C’s `timespec` works to how it actually works. The previous behavior was also buggy for timestamps strictly before the epoch but less than one second away from it, because two’s complement does not distinguish negative zero from positive zero. Differential Revision: https://phab.mercurial-scm.org/D11629

dirstate-v2: Only convert from SystemTime to Timestamp and not back Converting from Timestamp back to SystemTime was only used for equality comparison, but this can also be done on Timestamp values. Differential Revision: https://phab.mercurial-scm.org/D11631