implement `handle_push_solution` on `jd_server_sv2` + `bitcoin_core_sv2`

[plebhash]

blocked by

• Sv2 needs a submitBlock IPC method bitcoin/bitcoin#34626
• Add submitBlock(), misc. test improvements 2140-dev/bitcoin-capnp-types#12

[plebhash]

bitcoin/bitcoin#34644 merged

[plebhash]

Bitcoin Core v32 is scheduled for ~October 2026, so whenever Q3 rolls around we should add this issue to the board

[Sjors]

It would be good to have a working draft of this change to test against Bitcoin Core's master branch. Because otherwise, if anything is missing you'll have to wait another six months.

[plebhash]

hmm makes sense, we should plan for tackling this earlier cc @GitGab19