BIP127: Replace network_magic with BIP44 coin_type in ProofOfReserves message

[GarmashAlex]

This commit updates the ProofOfReserves message in the Protocol Buffers specification
to use BIP44 coin type IDs from SLIP-0044 instead of network magic values.

The changes include:

• Renaming the field from 'network_magic' to 'coin_type'
• Updating the comments to reference the SLIP-0044 registry
• Adding examples for Bitcoin mainnet (0x80000000) and Testnet (0x80000001)

[murchandamus]

Pinging the author: @stevenroose

[jonatack]

@stevenroose mind weighing in here, as BIP author?

[murchandamus]

@stevenroose: If you have a minute, could you take a look at this?

[jonatack]

This PR was opened one year ago today.

Friendly nudge to BIP author https://github.com/stevenroose if you can have a look here.

[murchandamus]

I’ve pinged @stevenroose out of band. I propose that we close this PR as "no interest", if there is no review here in the next two weeks. I have also asked @stevenroose, whether BIP127 should be moved to either Closed or Complete, because it doesn’t seem that it is still being actively worked on.

[stevenroose]

Yeah I don't think anyone is using the protocol buffers part from this BIP. I think I will make a PR to remove that part and then mark it as complete.

[stevenroose]

Please close this in favor of #2168.

[jonatack]

@GarmashAlex thanks for your proposal. Closing per the above feedback by the BIP author.