Restrict bitcoin amounts

[t-bast]

It doesn't make sense to exchange amounts that exceed the total bitcoin supply, so let's make that an explicit requirement.
Eclair has always enforced this requirement at the wire layer, where messages that use invalid bitcoin amounts are automatically rejected.

[TheBlueMatt]

Makes sense. Probably a good thing to do on most implementations to ensure overflows aren't possible.

[ariard]

Good to me, I verified hex are correct :)

[m-schmoock]

I know its pedantic, but when we limit we should use exact amount which would be:

• sat 0x775f059e40090 ( 2099999997690000 )
• msat 0x1d24b2df22a23200 ( 2099999997690000000 )
  ( https://en.bitcoin.it/wiki/Controlled_supply )

[TheBlueMatt]

I know its pedantic, but when we limit we should use exact amount which would be:

I don't see why? The point is that it avoids various internal number overflow checks, reducing it by some tiny % isn't going to change that?

[m-schmoock]

now that you put it that way I agree :D

[t-bast]

Merging this PR as we had acks from rust-lightning and c-lightning during yesterday's spec meeting.