Add CRLF injection protection for header values

Implement security validation to prevent HTTP header injection attacks:
- Reject header values containing \r or \n characters
- Add comprehensive test coverage for CRLF protection
- Replace multiline YAML test with proper rejection test

Security improvements:
- Validates header values to prevent header injection
- Clear warning messages when values are rejected
- Four new test cases covering LF, CR, CRLF, and multiline scenarios

This addresses a critical security concern where malicious headers
could be injected via newline characters in header values.

All 84 tests passing.

dist/index.js

@@ -61361,6 +61361,11 @@ function validateAndMaskHeaders(headers) {
         }
         // Convert value to string
         const stringValue = String(value);
+        // Validate header value to prevent CRLF/header injection
+        if (stringValue.includes('\r') || stringValue.includes('\n')) {
+            coreExports.warning(`Skipping header "${name}" because its value contains newline characters, which are not allowed in HTTP header values.`);
+            continue;
+        }
         validHeaders[name] = stringValue;
         // Mask sensitive headers in logs
         const lowerName = name.toLowerCase();