fix(BAMLAdapter): Use docstrings to describe BaseModels

[BenMcH]

This PR fixes an issue in which pydantic basemodels do not have their docstrings exposed to the generated signature as they do with other adapters.

Before:

All interactions will be structured in the following way, with the appropriate values filled in.

[[ ## input ## ]]
{input}

[[ ## complex ## ]]
Output field `complex` should be of type: {
  # Unique identifier
  id: int,
  details:   {
    # Full name of the patient
    name: string,
    age: int,
    address:     {
      street: string,
      city: string,
      country: "US" or "CA",
    } or null,
  },
  tags: string[],
  metadata: dict[string, string],
}

[[ ## completed ## ]]

After:

All interactions will be structured in the following way, with the appropriate values filled in.

[[ ## input ## ]]
{input}

[[ ## complex ## ]]
Output field `complex` should be of type: # Complex model docstring
{
  # Unique identifier
  id: int,
  # Patient Details model docstring
  # Multiline docstring support test
  details:   {
    # Full name of the patient
    name: string,
    age: int,
    # Patient Address model docstring
    address:     {
      street: string,
      city: string,
      country: "US" or "CA",
    } or null,
  },
  tags: string[],
  metadata: dict[string, string],
}

[[ ## completed ## ]]

Additionally closes #8657

[prrao87]

Thanks for the fix! Looking forward to seeing this merged and usable in DSPy soon 😄.

[isaacbmiller]

Thanks for submitting @BenMcH