Support BPCHAR

[jacobsvante]

Getting this error for a CHAR(2) column:

  × Couldn't register SQL type.
   ╭─[./spotpilot-db/queries/site.sql:6:1]
 6 │ --
 7 │ --! select_one: DbSite
   ·     ─────┬────
   ·          ╰── this query contains an unsupported type (name: country, type: bpchar)
 8 │ SELECT

I guess this is because BPCHAR is not mentioned here:

cornucopia/crates/cornucopia/src/type_registrar.rs

Lines 374 to 394 in d1229ae

	Kind::Simple => {
	let (rust_name, is_copy) = match *ty {
	Type::BOOL => ("bool", true),
	Type::CHAR => ("i8", true),
	Type::INT2 => ("i16", true),
	Type::INT4 => ("i32", true),
	Type::INT8 => ("i64", true),
	Type::FLOAT4 => ("f32", true),
	Type::FLOAT8 => ("f64", true),
	Type::TEXT | Type::VARCHAR => ("String", false),
	Type::BYTEA => ("Vec<u8>", false),
	Type::TIMESTAMP => ("time::PrimitiveDateTime", true),
	Type::TIMESTAMPTZ => ("time::OffsetDateTime", true),
	Type::DATE => ("time::Date", true),
	Type::TIME => ("time::Time", true),
	Type::JSON | Type::JSONB => ("serde_json::Value", false),
	Type::UUID => ("uuid::Uuid", true),
	Type::INET => ("std::net::IpAddr", true),
	Type::MACADDR => ("eui48::MacAddress", true),
	Type::NUMERIC => ("rust_decimal::Decimal", true),
	_ => {