ref/c: segwit_decode_addr_details: capture details and return

[switck]

kept same API, but added a less-opinionated interface, that will allow caller to detect bech32m/not, incorrect HRP and report details to users

[switck]

• changed API so encoding not exposed anymore
• my library usage of this function: https://github.com/switck/libngu/blob/1e08ec2410ca8ede438947c4e6f6f1edf1fe6587/ngu/codecs.c#L124