Add push_asset_amount to OpenChannelRequest and update validation logic

[bitwalt]

• Introduced push_asset_amount field in OpenChannelRequest struct to handle asset pushes in RGB channels.
• Updated validation to ensure push_asset_amount is only used with RGB channels and does not exceed asset_amount.
• Modified channel opening logic to calculate local and remote amounts based on push_asset_amount.
• Added tests for validating push_asset_amount functionality and error conditions.

Closes #67

[zoedberg]

Thanks, please address the requested changes

[bitwalt]

ok fixes should have been addressed, there was a problem on full-push case that required changes also in rust-lightning due to non-zero opener local balance

[zoedberg]

Please see the requested change. Also please add some more checks/actions (payments, close channel, spend on-chain) after opening the channel with a push amount

[bitwalt]

Test updated with more checks (keysend, closing, spending on-onchain)

[nicbus]

I think tests need to be further improved.

[zoedberg]

@bitwalt please address #69 (comment) and rebase the commit on top of the updated master

[bitwalt]

Changes has been addressed. Let me know if there are other required changes.
I was also thinking, could there be problems if one of the two nodes goes offline before the channel is confirmed, or during some phases of the channel opening ?

[zoedberg]

Changes has been addressed. Let me know if there are other required changes.

On my PC the test openchannel_push_asset_amount::openchannel_push_asset_amount sometimes fails with these logs:

[...]
sending spontaneously Some(50) of asset Some("rgb:hg2~fj1r-Rj0bDO2-Osm~ps~-nbb6kMa-sMsSRuk-cQI4fno") from node 0.0.0.0:35265 to 02e33febb985a2bbea42746ebfe31683db94e46e0c30f7a5aa9b382b81db1e7723
2026-03-16T15:07:36.295232Z  INFO request{uri=/keysend request_id=7a03f191-6749-4a1e-a8a9-61d124470318}: rgb_lightning_node: STARTED
2026-03-16T15:07:36.299751Z ERROR rgb_lightning_node::routes: ERROR: failed to send payment: RouteNotFound
2026-03-16T15:07:36.302716Z  INFO request{uri=/keysend request_id=7a03f191-6749-4a1e-a8a9-61d124470318 status_code=200 OK}: rgb_lightning_node: ENDED in 7.503876ms
checking payment 35daa64c4a17c405987688c8bc730bc478c5a2a76a001e2c1280492e9d5be9cc is Pending on node 0.0.0.0:35265
listing payments for node 0.0.0.0:35265
2026-03-16T15:07:36.312249Z  INFO request{uri=/listpayments request_id=d5aedde4-14c3-41a4-b3d7-b2383705f8ff}: rgb_lightning_node: STARTED
2026-03-16T15:07:36.312481Z  INFO request{uri=/listpayments request_id=d5aedde4-14c3-41a4-b3d7-b2383705f8ff status_code=200 OK}: rgb_lightning_node: ENDED in 246.023µs
payment found but with status: Failed

thread 'test::openchannel_push_asset_amount::openchannel_push_asset_amount' (2643288) panicked at src/test/mod.rs:675:10:
called `Option::unwrap()` on a `None` value

I was also thinking, could there be problems if one of the two nodes goes offline before the channel is confirmed, or during some phases of the channel opening ?

LDK should handle this, but feel free to do more tests/checks if you think there might be problems.