Discontinue dependency on Themis subpackages

[joe94]

This work will be rather non-trivial and this issue can likely be split into smaller ones. One important thing to consider will be to ensure the OpenTelemetry tracing feature is present in the replacements of xhttpserver and xhttpclient.
Sub-tacks for this issue:

• Switch to zap logger Switch to zap logger #181
• Use arrange to unmarshal config structs Use arrange to unmarshal config structs #182
• Use arrange servers Use arrange for servers #183
• Add back tracing feature Use future version of arrange to decorate server and client for tracing feature #184