LeadSquared sync now recovers automatically when a contact's cached lead
has been deleted or merged on the LeadSquared side. Previously the stale
lead id was never cleared, so every new conversation or contact update
for that contact failed with "Lead not found"
(`MXInvalidEntityReferenceException`) indefinitely.
## What changed
- Activity sync: on a "Lead not found" error while posting a
conversation/transcript activity, clear the cached `leadsquared_id`,
re-resolve the contact to a fresh lead, and retry the activity once
(guarded against loops and duplicate leads).
- Contact sync: on the same error while updating an existing lead, clear
the cached id and create a fresh lead instead.
- Fix `get_lead_id` to actually return early for unidentifiable contacts
(the guard previously fell through).
## How to reproduce
1. For a LeadSquared-enabled account, point a contact's cached lead id
at a lead that no longer exists in LeadSquared.
2. Update the contact, or create/resolve a conversation for it.
3. Before: the sync fails repeatedly with "Lead not found" and never
self-corrects. After: the stale id is cleared, a fresh lead is
resolved/created, and subsequent syncs reuse the healed id.
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Co-authored-by: Tanmay Deep Sharma <32020192+tds-1@users.noreply.github.com>
