feat(python,rust,cli): add SQL support for binary data and expand recognised SQL dtype strings

[alexander-beedie]

Adds SQL type support for Binary dtype, and recognition of additional PostgreSQL type strings such as double precision (Float64) and character varying (Utf8).

Example

The following now works:

import polars as pl

df = pl.DataFrame({
    "colx": [1, 2, 3],
    "coly": ["a", "b", "c"],
})

with pl.SQLContext( df=df, eager_execution=True ) as ctx:
    res = ctx.execute(
        """
        SELECT
          CAST(colx AS DOUBLE PRECISION) AS x_float,
          coly::varbinary AS y_binary,
        FROM df
        """
    )
    # ┌─────────┬───────────────┐
    # │ x_float ┆ y_binary      │
    # │ ---     ┆ ---           │
    # │ f64     ┆ binary        │
    # ╞═════════╪═══════════════╡
    # │ 1.0     ┆ [binary data] │
    # │ 2.0     ┆ [binary data] │
    # │ 3.0     ┆ [binary data] │
    # └─────────┴───────────────┘

res.to_dict(False)
# {
#   'x_float': [1.0, 2.0, 3.0], 
#   'y_binary': [b'a', b'b', b'c'],
# }