Changes for supporting GPT-5

[sashirestela]

Introduced the minimal reasoning effort value to optimize for fast responses in GPT-5 models (which support reasoning).

Introduced custom tool call type, which allows for freeform inputs to and outputs from the model when tool calling.

[dzikoysk]

Minimal reasoning effort is already supported, but it'd be also great to prioritize support for verbosity parameter - it's quite important for models from the GPT-5 family:

• https://platform.openai.com/docs/guides/latest-model#verbosity