Propagate build failures instead of silently continuing.

-    string|error crAuthHeader = buildCRAuthHeader(req);
-    if crAuthHeader is string {
-        outboundFHIRReq.setHeader("Authorization", crAuthHeader);
-    }
+    string crAuthHeader = check buildCRAuthHeader(req);
+    outboundFHIRReq.setHeader("Authorization", crAuthHeader);

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

    string crAuthHeader = check buildCRAuthHeader(req);
    outboundFHIRReq.setHeader("Authorization", crAuthHeader);

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@iol/iol-core/router.bal` around lines 152 - 155, The code silently ignores
errors from buildCRAuthHeader causing outbound requests to be sent without
Authorization; change the logic to fail fast: after calling
buildCRAuthHeader(check crAuthHeader), if it is an error propagate it (return or
throw) from the current function instead of continuing, otherwise set the header
with outboundFHIRReq.setHeader(crAuthHeader); reference the symbol
buildCRAuthHeader and the variable crAuthHeader to locate the change and ensure
the function's signature/caller supports propagating the error (add a returning
error path if needed).