Support MACADDR in Postgres

[mehcode]

https://docs.rs/mac_address/1.0.3/mac_address/struct.MacAddress.html

[abonander]

Type OID: 829
Array type OID: 1040

https://github.com/postgres/postgres/blob/master/src/include/catalog/pg_type.dat#L244-L248

Binary format: i8 i8 i8 i8 i8 i8 (literally just 6 bytes, can pass this straight to MacAddress::new())
https://github.com/postgres/postgres/blob/master/src/backend/utils/adt/mac.c#L161

Use mac_address::MacAddress::from_str to parse the text format.

We can also support the EUI format which is just 8 literal bytes:
https://github.com/postgres/postgres/blob/master/src/include/catalog/pg_type.dat#L260-L264
https://github.com/postgres/postgres/blob/master/src/backend/utils/adt/mac8.c#L295

However, mac_address doesn't support the extended format so we can't do parsing of the text format. Maybe we should just implement our own wrappers instead; it wouldn't be that difficult.

[mehcode]

https://docs.rs/eui48/0.4.6/eui48/struct.MacAddress.html

This seems to support both kinds.

[abonander]

The MacAddress type in that crate is still just the 48-bit addresses though.

[EverWinter23]

From @mehcode on discord:

• Postgres supports both macaddr and macaddr8 type
• rust-postgres driver however only supports macaddr type using the eui48 crate
• eui48 and mac_address crates only support the 6-byte macaddr type

Recommended way-- would be to implement support for macaddr using either eui48 or mac_address (no preference).

If we want to support macaddr8, we should add support for the type to the crate that was used.