feat(database): add find cursor iteration

[KilianBoute]

Description

This change adds cursor-style iteration support for database find operations through the new CursorResultInterface. Previously, consumers could only decode the entire result set at once with All(), which meant a single malformed document could fail the entire query result.

With per-document iteration (Next, Decode, and Close), callers can now handle decode failures on individual records while continuing to process valid documents. This improves resilience for workloads that operate on partially inconsistent or evolving data without sacrificing the rest of the result set.

The MongoDB implementation and mock database were both updated to support the new interface, ensuring consistent behavior between production code and tests. Additional test coverage verifies that:

• iteration continues when a single document fails to decode
• cursor errors are preserved and surfaced correctly
• mock behavior matches real cursor semantics

Overall, this improves fault tolerance, makes data processing workflows more flexible, and enables more realistic testing of streaming query behavior.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 18 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/database/mongodb.go	0.00%	14 Missing ⚠️
pkg/database/mock.go	81.81%	2 Missing and 2 partials ⚠️

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