feat: RFC 9457 compatible (#10)

* feat: RFC 9457 compatible

* fix: test content-type (resolve: discussion_r1936938314)

* fix: validation as package var (resolve: discussion_r1936947547)

* fix: handle response encode error (resolve discussion_r1936947554)

* feat: expanding problem details

* fix: adjust typo and handle mutex

* fix: use default title based on status code

* fix: mu.RLock for getters

feat: remove chi dependency (#8)

fix: adding chartset to the response (#7)

hotfix: updating deps for security