#30 - add graphql support for custom objects

[arthanson]

Fixes: #30

Custom objects are now queryable through NetBox's GraphQL API at /graphql/, alongside built-in NetBox models. Each CustomObjectType gets two root query fields: (single object by id) and _list (paginated list).

How it works

• A Strawberry type is generated at runtime for each CustomObjectType, mirroring how the models themselves are generated.
• The plugin contributes its Query via the standard graphql_schema resource, so NetBox merges it into the global schema during ready() — after dynamic models are built.
• Object-level view permissions are enforced (types inherit NetBox's BaseObjectType).

Field mapping

• Scalars → natural GraphQL types (String, Int, Decimal, Boolean, Date, DateTime, JSON, [String]).
• Object / multi-object (incl. polymorphic) → a shared CustomObjectRelatedObjectType (id, object_type, display, url).
• Base fields: id, display, created, last_updated, tags.

Live schema & caching

Custom object types can be created, edited, and deleted at runtime, so the GraphQL schema can't be built once at boot like NetBox's. A small view patch swaps in a per-request, per-process schema that tracks the database - runtime changes appear without a NetBox restart, across all worker processes, with no cross-process messaging.

• Change detection: each request computes a cheap signature — row counts + max cache_timestamp/last_updated over CustomObjectType/CustomObjectTypeField (two aggregate queries). cache_timestamp is bumped on every structural change, and counts catch adds/removes, so any worker notices a change on its next request.
• Schema cache: the assembled schema is cached per process and rebuilt only when the signature changes. The hot path (unchanged) is lock-free; rebuilds are single-flight (one thread rebuilds while others keep serving the current schema instead of blocking).
• Per-type cache: each COT's Strawberry type is memoized by (id, cache_timestamp), so a rebuild triggered by one type reuses every other type's already-built definition instead of regenerating all of them.