plugin: fix gosec G115 integer overflow warnings (#7799)

Fix integer overflow conversion warnings (G115) by adding appropriate
suppressions where values are provably bounded.

Fixes: https://github.com/coredns/coredns/issues/7793

Changes:
- Updated 56 G115 annotations to use consistent // #nosec G115 format
- Added 2 //nolint:gosec suppressions for conditional expressions
- Removed G115 exclusion from golangci.yml (now explicitly handled per-line)

Suppressions justify why each conversion is safe (e.g., port numbers
are bounded 1-65535, DNS TTL limits, pool lengths, etc.)

Signed-off-by: Azeez Syed <syedazeez337@gmail.com>

plugin/rewrite/ttl.go

@@ -199,7 +199,7 @@ func isValidTTL(v string) (uint32, uint32, bool) {
 			// reject invalid range
 			return 0, 0, false
 		}
-		return uint32(min), uint32(max), true
+		return uint32(min), uint32(max), true // #nosec G115 -- min/max parsed with 32-bit limit
 	}
 	return 0, 0, false
 }