Support openai >= 2.0.0 or make it an optional (`extra`) dependency

[dmugtasimov]

All new OpenAI features are not available because of marker-pdf (>=1.8.2,<2.0.0) limitations.

Please, support openai >= 2.0.0 or at least relax requirement or move open to an optional (extra) dependency.

For example I need prompt_cache_retention keyword argument to support corresponding feature, but I am getting error:

TypeError: Responses.parse() got an unexpected keyword argument 'prompt_cache_retention'

And I can't upgrade because of marker-pdf limitation:

(regpilot-backend-py3.13) dmugtasimov@dmugtasimov-Latitude-3540:~/gitrep/ceet/mvp_copilot_green_energy/django_backend$ poetry add 'openai>=2.8.0'

Updating dependencies
Resolving dependencies... (1.3s)

Because no versions of marker-pdf match >1.8.2,<1.8.3 || >1.8.3,<1.8.4 || >1.8.4,<1.8.5 || >1.8.5,<1.9.0 || >1.9.0,<1.9.1 || >1.9.1,<1.9.2 || >1.9.2,<1.9.3 || >1.9.3,<1.10.0 || >1.10.0,<1.10.1 || >1.10.1,<2.0.0
 and marker-pdf (1.8.3) depends on openai (>=1.65.2,<2.0.0), marker-pdf (>1.8.2,<1.8.4 || >1.8.4,<1.8.5 || >1.8.5,<1.9.0 || >1.9.0,<1.9.1 || >1.9.1,<1.9.2 || >1.9.2,<1.9.3 || >1.9.3,<1.10.0 || >1.10.0,<1.10.1 || >1.10.1,<2.0.0) requires openai (>=1.65.2,<2.0.0).
And because marker-pdf (1.8.4) depends on openai (>=1.65.2,<2.0.0), marker-pdf (>1.8.2,<1.8.5 || >1.8.5,<1.9.0 || >1.9.0,<1.9.1 || >1.9.1,<1.9.2 || >1.9.2,<1.9.3 || >1.9.3,<1.10.0 || >1.10.0,<1.10.1 || >1.10.1,<2.0.0) requires openai (>=1.65.2,<2.0.0).
And because marker-pdf (1.8.5) depends on openai (>=1.65.2,<2.0.0)
 and marker-pdf (1.9.0) depends on openai (>=1.65.2,<2.0.0), marker-pdf (>1.8.2,<1.9.1 || >1.9.1,<1.9.2 || >1.9.2,<1.9.3 || >1.9.3,<1.10.0 || >1.10.0,<1.10.1 || >1.10.1,<2.0.0) requires openai (>=1.65.2,<2.0.0).
And because marker-pdf (1.9.1) depends on openai (>=1.65.2,<2.0.0)
 and marker-pdf (1.9.2) depends on openai (>=1.65.2,<2.0.0), marker-pdf (>1.8.2,<1.9.3 || >1.9.3,<1.10.0 || >1.10.0,<1.10.1 || >1.10.1,<2.0.0) requires openai (>=1.65.2,<2.0.0).
And because marker-pdf (1.9.3) depends on openai (>=1.65.2,<2.0.0)
 and marker-pdf (1.10.0) depends on openai (>=1.65.2,<2.0.0), marker-pdf (>1.8.2,<1.10.1 || >1.10.1,<2.0.0) requires openai (>=1.65.2,<2.0.0).
And because marker-pdf (1.10.1) depends on openai (>=1.65.2,<2.0.0)
 and marker-pdf (1.8.2) depends on openai (>=1.65.2,<2.0.0), marker-pdf (>=1.8.2,<2.0.0) requires openai (>=1.65.2,<2.0.0).
So, because regpilot-backend depends on both marker-pdf (>=1.8.2,<2.0.0) and openai (>=2.8.0), version solving failed.