fix: serialize datetime fields when creating queue items (#670)

[radu-mocanu]

Summary

• queue items with defer_date, due_date, or risk_sla_date no longer raise TypeError: Object of type datetime is not JSON serializable
• applies to create_item, create_items, start_transaction_item, and complete_transaction_item

Why

Fixes #670

model_dump was called without mode="json", so the field_serializer configured to convert datetime to ISO 8601 never fired and httpx received raw datetime objects it could not encode.

Development Packages

uipath

[project]
dependencies = [
  # Exact version:
  "uipath==2.10.60.dev1016076290",

  # Any version from PR
  "uipath>=2.10.60.dev1016070000,<2.10.60.dev1016080000"
]

[[tool.uv.index]]
name = "testpypi"
url = "https://test.pypi.org/simple/"
publish-url = "https://test.pypi.org/legacy/"
explicit = true

[tool.uv.sources]
uipath = { index = "testpypi" }

uipath-platform

[project]
dependencies = [
  # Exact version:
  "uipath-platform==0.1.41.dev1016076290",

  # Any version from PR
  "uipath-platform>=0.1.41.dev1016070000,<0.1.41.dev1016080000"
]

[[tool.uv.index]]
name = "testpypi"
url = "https://test.pypi.org/simple/"
publish-url = "https://test.pypi.org/legacy/"
explicit = true

[tool.uv.sources]
uipath-platform = { index = "testpypi" }