Implement the duration format validator

[Stranger6667]

No description provided.

[floriantz]

I have taken a look to see if I could implement this but this might end-up being more difficult than expected.

The json-schema spec duration format is based on ISO8601:

• https://json-schema.org/draft/2020-12/json-schema-validation.html#rfc.section.7.3.1
• https://datatracker.ietf.org/doc/html/rfc3339#appendix-A

From what I can see, jsonschema-rs relies on the chrono for any time related format validation, but it is currently missing a way to parse and validate ISO8601 Durations.
There was some work on this at some point but it seems it has not moved forward in a while (PR Discussion on the implementation in chrono here)

I've tried to look for an already battle-tested Rust parser for ISO8601 Durations, but I did not manage to find one thus far. So implementing the duration format would also entail implementing a proper parser which could prove tricky since I expect jsonschema-rs should be able to deal with untrusted input.

Since I spent some time researching this I wanted to share it here, which can hopefully clarify the issue a little.

[syheliel]

I found that crate iso8601 provide the api for duration and open a PR #276.

[Stranger6667]

Thank you very much!