Fix node deletion with unidirectional optional relationship

[LucasG0]

Fixes #5619

• Store unidirectional relationships within SchemaBranch
• Then check for them while deleting a node

[codspeed-hq]

CodSpeed Performance Report

Merging #5783 will degrade performances by 42.79%

_{Comparing lgu-fix-delete-peer (9b24b42) with stable (e78eeae)}

Summary

❌ 1 regressions
✅ 10 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	test_schemabranch_process	411.3 ms	718.9 ms	-42.79%