[tests] implement DinD test for SRP TC 2.6 Name Compression

[jwhui]

This commit implements the Thread 1.3 certification test case 2.4. [1.3] [CERT] Key Lease (1_3_SRP_TC_4) within the Docker-in-Docker testing framework.

Specifically, this adds:

1. dind_srp_tc_4.exp: The Expect script executing the multi-node test procedure across BR_1 (DUT), ED_1 (Node 4), ED_2 (Node 5), and the adjacent infrastructure link test client.
2. Hooked dind_srp_tc_4.exp into test_dind_dns_sd.sh runner script.

The test verifies that an SRP server correctly enforces key leases by rejecting service name and hostname takeovers when a service lease has expired but the associated key lease remains active (returning YXDomain). It also verifies that takeovers succeed once the key lease fully expires.

[jwhui]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces three new integration test scripts (dind_srp_tc_4.exp, dind_srp_tc_5.exp, and dind_srp_tc_6.exp) to verify SRP Key Lease, SRP KEY Record Inclusion/Omission, and SRP Name Compression behaviors respectively. Additionally, the main test runner script test_dind_dns_sd.sh is updated to execute these new test cases. There are no review comments, and I have no feedback to provide.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.78%. Comparing base (2b41187) to head (2d88057).
⚠️ Report is 1517 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #3411       +/-   ##
===========================================
- Coverage   55.77%   44.78%   -11.00%     
===========================================
  Files          87      143       +56     
  Lines        6890    17277    +10387     
  Branches        0     1417     +1417     
===========================================
+ Hits         3843     7737     +3894     
- Misses       3047     8995     +5948     
- Partials        0      545      +545     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.