Feat: Support multipart/mixed (#7155)

* feat(): support multipart mixed

fix: support vars interpolation on mixed multi-part

Update packages/bruno-electron/src/ipc/network/interpolate-vars.js

Co-authored-by: Timon <39559178+Its-treason@users.noreply.github.com>

refactor: use startsWith

feat: best effort for other multipart/* contentypes

* feat: enhance variable interpolation for multipart requests

- Updated `interpolateVars` function to support interpolation in multipart/form-data and multipart/mixed requests.
- Added handling for empty multipart arrays and parts with missing or undefined values.
- Improved type checks for content types to ensure proper interpolation behavior.

Includes new tests to validate the interpolation functionality for multipart requests.

* fix: normalize error handling in sendRequest and improve test reliability

---------

Co-authored-by: Alfonso Presa <alfonso-presa@users.noreply.github.com>

packages/bruno-cli/src/runner/interpolate-vars.js

@@ -96,7 +96,7 @@ const interpolateVars = (request, envVariables = {}, runtimeVariables = {}, proc
           value: _interpolate(d?.value)
         }));
       }
-    } else if (contentType === 'multipart/form-data') {
+    } else if (contentType.startsWith('multipart/')) {
       if (Array.isArray(request?.data) && !isFormData(request.data)) {
         try {
           request.data = request?.data?.map((d) => ({