ESD-1689: Test BGP JSON validation errors at a non-zero connection index

[Phil-Browne]

Adds test coverage proving parseBGPConnections reports the correct connection index when the bad-type field is on a non-first entry in a multi-connection bgpConnections array, not just index 0. Every existing case only ever exercised a single-entry array, so the index arithmetic at a non-zero position was never proven correct.

• Two new subtests in TestParseVRouterConfigBGP: one with a bad field on the second of two connections (index 1), one on the third of three (index 2).
• Test-only change, no production code touched.

Verified the assertions are load-bearing by temporarily swapping the j/ifaceIndex arguments in production code and confirming both new subtests fail, then reverting.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.50%. Comparing base (f266dc2) to head (f94b397).

Additional details and impacted files

@@ Coverage Diff @@## main #548 +/- ##
=======================================
Coverage 79.50% 79.50% =======================================
Files 193 193 Lines 18859 18859 =======================================
Hits 14993 14993 Misses 2818 2818 Partials 1048 1048 

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[Copilot]

Pull request overview

Adds targeted regression coverage to ensure parseBGPConnections reports the correct BGP connection index in JSON type-validation errors when the invalid field occurs at a non-zero position within a multi-entry bgpConnections array (e.g., index 1 or 2), rather than only exercising index 0.

Changes:

• Adds a subtest where the second of two BGP connections contains a wrong-typed shutdown field and asserts the error reports connection index 1.
• Adds a subtest where the third of three BGP connections contains a wrong-typed medIn field and asserts the error reports connection index 2.