FI-3223: Ensure Request Entity Verb Is Always Downcased

[vanessuniq]

Summary

This PR ensures that the verb attribute of the Request entity is consistently converted to lowercase during instantiation from all sources (Hamani, HTTP responses, or FHIR client).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.06%. Comparing base (f7ca46a) to head (cd27728).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #554   +/-   ##
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  Coverage   84.06%   84.06%           
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  Files         262      262           
  Lines       11410    11410           
  Branches     1254     1254           
=======================================
  Hits         9592     9592           
  Misses       1808     1808           
  Partials       10       10           

Flag	Coverage Δ
backend	92.19% <ø> (ø)
frontend	79.33% <ø> (ø)

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