Reuse SMART search integration fixture

[mikaelweave]

Summary

• Isolates the SMART search integration-test changes from the e2e-parallelization experiment branch.
• SMART search tests previously recreated fixture/seeding per test method; this reuses a shared search fixture context.
• The shared context is keyed by FHIR version + data store and disposed at process exit because custom xUnit synthetic fixture instances do not have normal fixture lifetime management.
• Mutation tests use unique IDs; update tests create then update the same unique ID.

Validation

• Diff versus main includes only test\Microsoft.Health.Fhir.Shared.Tests.Integration\Features\Smart\SmartSearchTests.cs.
• git diff --check and git diff --check origin/main...HEAD passed.
• dotnet build test\Microsoft.Health.Fhir.R4.Tests.Integration\Microsoft.Health.Fhir.R4.Tests.Integration.csproj -f net9.0 passed (Build succeeded in 149.5s).
• Local R4 SQL SmartOnFhir shard on this split branch passed: 63/63 succeeded, 0 failed, test duration 68.5s, including build 156.5s.
• Source experiment branch local R4 SQL SmartOnFhir result: 63/63 passed in about 60.1s test duration / 83.5s including build.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.34%. Comparing base (ee554e9) to head (3828873).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5588   +/-   ##
=======================================
  Coverage   77.33%   77.34%           
=======================================
  Files         996      996           
  Lines       36534    36539    +5     
  Branches     5538     5539    +1     
=======================================
+ Hits        28255    28260    +5     
+ Misses       6912     6908    -4     
- Partials     1367     1371    +4     

see 9 files with indirect coverage changes

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[feordin]

It seems like we usually put fixtures in their own file, rather than with the test cases. This is a suggestion, just to match the rest of the code base.