Remove chrono dependency

[frozolotl]

With this PR, typst-cli uses time, same as typst.
This should reduce compile times by a bit.

[laurmaedje]

This was attempted before, but then reverted because it caused issues.

The time crate fails on Unix when retrieving the local offset while there are multiple threads because it is unsound. Chrono, on the other hand, parses the timezone information itself instead of using system APIs, circumventing the problem. See also time issue.

[frozolotl]

Interesting, I was under the assumption it was fixed already. It seems to have simply worked because my test document was compiled on one thread only.