feat: Support for multi-unit leases via Lease Item table

[iamtalib13]

PR Description:

Context:
Currently, the Lease DocType is restricted to a single property linked in the header. Large property managers
often need to link additional units (such as parking spaces or storage) to a single lease agreement without the
overhead of creating separate documents for each unit.

Implementation Details:
Following a hybrid approach to ensure minimal disruption to the existing workflow and naming conventions:

• Metadata Changes: Added an optional property_unit field to the Lease Item child table.
• Core Logic (lease.py):
  • Refactored validate to perform conflict checks on all unique properties (Header + Table).
  • Updated on_submit to trigger status updates ("On Lease") and generate "Handover" checklists for every
    linked property.
• UI Enhancements (lease.js): Added company-based filters for the new property_unit field.

Key Highlights:

• Backward Compatible: Existing single-unit leases and current data remain unaffected.
• Naming Intact: The Lease ID still follows the {property}-{#####} format based on the primary header unit.
• Automated Validation: Prevents double-leasing of any unit involved in the agreement.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 7 complexity · 0 duplication

Metric	Results
Complexity	7
Duplication	0

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