Fix to-json-type

[svilupp]

• Removed unnecessary printing to stdout during precompilation in precompile.jl.
• Fixed a "bug-waiting-to-happen" in tool use. to_json_type now enforces users to provide concrete types, because abstract types cannot be deserialized by JSON3.
• Flowed through a bug fix in StreamCallback where the usage information was being included in the response even when usage=nothing. Lower bound of StreamCallbacks was bumped to 0.5.1.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.02%. Comparing base (f73e683) to head (a58a567).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #248      +/-   ##
==========================================
- Coverage   92.03%   92.02%   -0.02%     
==========================================
  Files          49       49              
  Lines        4771     4776       +5     
==========================================
+ Hits         4391     4395       +4     
- Misses        380      381       +1     

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