Move `ibc-testkit` integration tests into `tests-integration` directory

[seanchen1991]

Closes: #1232

Description

---

PR author checklist:

• [ ] Added changelog entry, using unclog.
• [ ] Added tests.
• [ ] Linked to GitHub issue.
• [ ] Updated code comments and documentation (e.g., docs/).
• [ ] Tagged one reviewer who will be the one responsible for shepherding this PR.

Reviewer checklist:

• [ ] Reviewed Files changed in the GitHub PR explorer.
• [ ] Manually tested (in case integration/unit/mock tests are absent).

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 10.00000% with 18 lines in your changes are missing coverage. Please review.

Project coverage is 65.56%. Comparing base (2679767) to head (a2174a8).

Files	Patch %	Lines
ibc-testkit/src/utils/mod.rs	0.00%	18 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1233 +/- ## ========================================== - Coverage 67.33% 65.56% -1.77% ========================================== Files 234 234 Lines 23547 23519 -28 ========================================== - Hits 15855 15421 -434 - Misses 7692 8098 +406 ```

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