$import can handle merge throttling

[brendankowitz]

Description

This pull request adds improved handling for SQL throttling errors during resource import operations in the SQL Server FHIR data store. Now, when the system detects that concurrent calls are above optimal levels, it will back off for a randomized delay, reducing the chance of repeated throttling and improving system stability.

Error handling improvements:

• Added logic to detect SQL throttling errors (MergeResourcesConcurrentCallsIsAboveOptimal) in ImportResourcesAsync, introducing a randomized delay and warning log before retrying, to better handle high-concurrency scenarios.

Related issues

Addresses AB#177510.

Testing

Run several large scale $import tests, no failures

FHIR Team Checklist

• Update the title of the PR to be succinct and less than 65 characters
• Add a milestone to the PR for the sprint that it is merged (i.e. add S47)
• Tag the PR with the type of update: Bug, Build, Dependencies, Enhancement, New-Feature or Documentation
• Tag the PR with Open source, Azure API for FHIR (CosmosDB or common code) or Azure Healthcare APIs (SQL or common code) to specify where this change is intended to be released.
• Tag the PR with Schema Version backward compatible or Schema Version backward incompatible or Schema Version unchanged if this adds or updates Sql script which is/is not backward compatible with the code.
• When changing or adding behavior, if your code modifies the system design or changes design assumptions, please create and include an ADR.
• CI is green before merge
• Review squash-merge requirements

Semver Change (docs)

Patch|Skip|Feature|Breaking (reason)