fix: Avro map deterministic encoding

[radkawar]

Update encode_internal function to sort map entries by key before encoding, ensuring deterministic output.

[Kriskras99]

Hi @radkawar, why do you need this? This will severely degrade encoding performance, and the specification gives no guarantees on the key order.

[martin-g]

I agree with @Kriskras99 that this is not a good idea.
It will even break interop with other SDKs.