Derive Macro PyFieldDesc 

#[derive(PyFieldDesc)]
{
    // Attributes available to this derive:
    #[dbn]
}

Derive macro for field descriptions exposed to Python.

Supports the following dbn attributes:

• c_char: indicates the field dtype should be a single-character string rather than an integer
• encode_order: overrides the position of the field in the ordered list
• fixed_price: indicates this is a fixed-precision field
• skip: indicates this field should be hidden
• unix_nanos: indicates this is a UNIX nanosecond timestamp field