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/nomad/helpers.go

@@ -11,7 +11,7 @@ func addSRVRecord(m *dns.Msg, s *api.ServiceRegistration, header dns.RR_Header,
 	srvRecord := &dns.SRV{
 		Hdr:      header,
 		Target:   originalQName,
-		Port:     uint16(s.Port),
+		Port:     uint16(s.Port), // #nosec G115 -- port numbers are bounded (1-65535)
 		Priority: 10,
 		Weight:   10,
 	}

plugin/nomad/setup.go

@@ -19,7 +19,7 @@ func init() { plugin.Register(pluginName, setup) }
 // for parsing any extra options the nomad plugin may have. The first token this function sees is "nomad".
 func setup(c *caddy.Controller) error {
 	n := &Nomad{
-		ttl:     uint32(defaultTTL),
+		ttl:     uint32(defaultTTL), // #nosec G115 -- defaultTTL is a constant that fits in uint32
 		clients: make([]*nomad.Client, 0),
 		current: -1,
 	}