fix(mdns): Fix potential mem issue with scheduled packets #920
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Closes #917
Fixes memory leaks and use-after-free in mDNS question handling by ensuring dynamically allocated strings are freed when questions are discarded early.
Changes:
Stop freeing domain: q->domain points to MDNS_DEFAULT_DOMAIN, so it is not freed.
Switch to dynamic allocations in (Allocate host, service, and proto with mdns_mem_strndup() and set own_dynamic_memory = true)
Add cleanup in early discard paths:
Prevents leaks when questions are discarded before being queued (duplicates, NULL values, or early removal). Ensures consistency with the own_dynamic_memory flag and avoids accessing freed memory.
This aligns with the pattern used in
_mdns_free_tx_packet()for cleaning up dynamically allocated question fields.