[analyze_memory] Fix mDNS packet buffer miscategorized as wifi_config

Move `packet$` pattern from `wifi_config` to `mdns_lib` category.
The `packet$` static buffer is the mDNS packet assembly buffer used
by ESP-IDF's mDNS component, not a WiFi config symbol. This was
causing 1,460 B of mDNS RAM to appear under wifi_config in
ethernet-only builds.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

esphome/analyze_memory/const.py

@@ -256,7 +256,7 @@ SYMBOL_PATTERNS = {
     "ipv6_stack": ["nd6_", "ip6_", "mld6_", "icmp6_", "icmp6_input"],
     # Order matters! More specific categories must come before general ones.
     # mdns must come before bluetooth to avoid "_mdns_disable_pcb" matching "ble_" pattern
-    "mdns_lib": ["mdns"],
+    "mdns_lib": ["mdns", "packet$"],
     # memory_mgmt must come before wifi_stack to catch mmu_hal_* symbols
     "memory_mgmt": [
         "mem_",
@@ -794,7 +794,6 @@ SYMBOL_PATTERNS = {
         "s_dp",
         "s_ni",
         "s_reg_dump",
-        "packet$",
         "d_mult_table",
         "K",
         "fcstab",