chore: made pull and rehydrate a sequential process (#40407)

## Description
> [!TIP]  
> _Add a TL;DR when the description is longer than 500 words or
extremely technical (helps the content, marketing, and DevRel team)._
>
> _Please also include relevant motivation and context. List any
dependencies that are required for this change. Add links to Notion,
Figma or any other documents that might be relevant to the PR._


Fixes #  
_or_  
Fixes `Issue URL`
> [!WARNING]  
> _If no issue exists, please create an issue first, and check with the
maintainers if the issue is valid._

## Automation

/ok-to-test tags="@tag.Git"

### 🔍 Cypress test results
<!-- This is an auto-generated comment: Cypress test results  -->
> [!TIP]
> 🟢 🟢 🟢 All cypress tests have passed! 🎉 🎉 🎉
> Workflow run:
<https://github.com/appsmithorg/appsmith/actions/runs/14701656082>
> Commit: 83f2303ccb3b7456cbf0a78f64aea315df3158b4
> <a
href="https://internal.appsmith.com/app/cypress-dashboard/rundetails-65890b3c81d7400d08fa9ee5?branch=master&workflowId=14701656082&attempt=1"
target="_blank">Cypress dashboard</a>.
> Tags: `@tag.Git`
> Spec:
> <hr>Mon, 28 Apr 2025 07:23:20 UTC
<!-- end of auto-generated comment: Cypress test results  -->


## Communication
Should the DevRel and Marketing teams inform users about this change?
- [ ] Yes
- [ ] No


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Refactor**
- Improved the way certain asynchronous operations are combined during
artifact import and synchronization processes, resulting in more
efficient handling of related tasks. No changes to user-facing features
or interfaces.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

app/server/appsmith-server/src/main/java/com/appsmith/server/git/central/CentralGitServiceCEImpl.java

@@ -2014,7 +2014,7 @@ public class CentralGitServiceCEImpl implements CentralGitServiceCE {
                     Mono<ArtifactExchangeJson> artifactExchangeJsonMono = mergeStatusDTOMono.flatMap(status ->
                             gitHandlingService.reconstructArtifactJsonFromGitRepository(jsonTransformationDTO));
 
-                    return Mono.zip(mergeStatusDTOMono, artifactExchangeJsonMono);
+                    return mergeStatusDTOMono.zipWhen(mergeStatusDTO -> artifactExchangeJsonMono);
                 })
                 .flatMap(tuple -> {
                     MergeStatusDTO status = tuple.getT1();

app/server/appsmith-server/src/main/java/com/appsmith/server/git/common/CommonGitServiceCEImpl.java

@@ -1837,7 +1837,7 @@ public class CommonGitServiceCEImpl implements CommonGitServiceCE {
                                 status -> commonGitFileUtils.reconstructArtifactExchangeJsonFromGitRepoWithAnalytics(
                                         workspaceId, baseArtifactId, repoName, branchName, artifactType));
 
-                        return Mono.zip(pullStatusMono, artifactExchangeJsonMono);
+                        return pullStatusMono.zipWhen(mergeStatusDTO -> artifactExchangeJsonMono);
 
                     } catch (IOException e) {
                         return Mono.error(new AppsmithException(AppsmithError.GIT_FILE_SYSTEM_ERROR, e.getMessage()));