Generator fails on type: array without items even though it's valid in JSON Schema 2020-12 / OpenAPI 3.1

Describe the bug
When a schema has "type": "array" without an "items" field, the generator fails to produce a property for it. In JSON Schema 2020-12 (used by OpenAPI 3.1), omitting items is valid and means "array of any type". The generator should treat it as equivalent to "items": {} (i.e., generate a List[Any] property) rather than silently failing.

OpenAPI Spec File
We encountered this in two forms:
Case 1 — bare array with no constraints:

{
  "type": "array",
  "description": "Array of objects representing a row of metrics data - can be any format."
}

Case 2 — array with maxItems but no items:

{
  "anyOf": [
    { "type": "array", "maxItems": 0 },
    { "type": "object", "properties": { "tag": { "type": "array", "items": { "type": "string" } } } }
  ]
}

In both cases the generator silently skips the schema (or the anyOf branch) without an error. Adding ["items": {}] to each fixes the generation.

Expected behaviour: {"type": "array"} (with or without other constraints like maxItems) should generate a List[Any] property, consistent with how JSON Schema 2020-12 defines it.

Desktop (please complete the following information):

• OS: Ubuntu 24.04.3 LTS
• Python Version: 3.12.3
• openapi-python-client 0.28.1
• OpenAPI version: 3.1.1 (JSON Schema 2020-12)

Inizia tracciando il modo in cui il generatore gestisce gli schemi di array e i rami anyOf quando items è assente, usando come input i due schemi nell'issue. Aggiungi una copertura di regressione per gli array semplici e per gli array con maxItems, quindi esegui il generatore e conferma che entrambi producano una proprietà List[Any] invece di essere ignorati.