feat(nxos): add show ip ospf neighbors parser

[behrang-t]

NX-OS show ip ospf neighbors summary output needs a dedicated parser for structured neighbor data.

This PR adds ShowIpOspfNeighbors with its schema, parser registry entry, fixtures, regression tests and changelog.

The parser extracts the process, VRF, total neighbor count, interface, neighbor router ID, priority, state, role, uptime and address. Neighbors are grouped by interface so the same router ID on separate links is preserved.

An explicit zero-neighbor summary produces structured output. Completely empty input raises SchemaEmptyParserError. Missing counts, duplicate neighbors on the same interface and mismatches between the declared count and parsed rows raise errors rather than returning incomplete results.

Validation:

• All 9 focused regression tests passed, including command-based parser lookup.
• The official folder-based runner passed all 5 golden fixtures and 1 empty fixture.
• Successfully parsed 20 recorded NX-OS outputs from 7 lab devices.
• git diff --cached --check passed.

make json was executed. The committed registry diff retains only the new OSPF command entry, excluding unrelated generator changes.

[Sripadvallabh]

Fix comments & click re-review