Functions with record array paraments

Nobody has claimed this yet.

I'm trying to invoke a function with a signature like this:
```
CREATE OR REPLACE FUNCTION "ns"."test"(p1 "ns"."my_type"[])
```
It results in the following exception being raised:
```
Traceback (most recent call last):
File "asyncpg/protocol/prepared_stmt.pyx", line 168, in asyncpg.protocol.protocol.PreparedStatementState._encode_bind_msg
File "asyncpg/protocol/codecs/base.pyx", line 206, in asyncpg.protocol.protocol.Codec.encode
File "asyncpg/protocol/codecs/array.pyx", line 115, in asyncpg.protocol.protocol.array_encode
File "asyncpg/protocol/codecs/array.pyx", line 115, in asyncpg.protocol.protocol.array_encode
TypeError: a sized iterable container expected (got type 'dict')

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
buffer, _, self._exhausted = await protocol.bind_execute(
File "asyncpg/protocol/protocol.pyx", line 183, in bind_execute
File "asyncpg/protocol/prepared_stmt.pyx", line 197, in asyncpg.protocol.protocol.PreparedStatementState._encode_bind_msg
asyncpg.exceptions.DataError: invalid input for query argument $1: {'holiday_center': '123', 'observed_on':... (a sized iterable container expected (got type 'dict'))
```

How do I invoke such a function?

Start with the SQL function signature and the array encoder shown in asyncpg/protocol/codecs/array.pyx, then trace how the argument reaches asyncpg/protocol/prepared_stmt.pyx. Reproduce the call with the record-array parameter and compare the accepted input shape with the reported dict error; done means the function can be invoked successfully and the behavior is covered or clearly documented.

Written by the indexing model from the issue text.