Object.Update and SetModTime left the in-memory modtime at the
source's nanosecond precision, while the server stores milliseconds.
Afterwards the in-memory state did not match what a fresh List would
report, which broke wrappers that compare modtimes (e.g. the hasher
backend's fingerprint, which made it lose track of hashes whenever a
file was replaced).
The SDK serializes modtimes as UnixMilli and NewIncompleteFile
already rounds to milliseconds, so Put and the chunked upload path
are unaffected. Round the modtime to milliseconds in Update and
SetModTime too, so every path holds the same value the server
returns, without needing to re-read the metadata from the server
after upload.
Fixes#9308
Nick Craig-Wood
2eaaf91b83