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/etcd/etcd.go

@@ -190,7 +190,7 @@ func (e *Etcd) TTL(kv *mvccpb.KeyValue, serv *msg.Service) uint32 {
 				leaseTTL = maxTTL64
 			}
 
-			etcdTTL = uint32(leaseTTL)
+			etcdTTL = uint32(leaseTTL) // #nosec G115 -- leaseTTL is bounded by minTTL64/maxTTL64
 		}
 	}