integration tests: all Electrum components inside an interpreter

[bitromortac]

Currently, the tests have the same prerequisites as the regtest tests and can only be executed in isolation (one test at a time per pytest/unittest call). These tests are intended as an a supplement for the regtests. Depends on #7509.

Advantages:

• launches several Electrum components to interact on a regtest network in a single interpreter
• eases development, as one can debug into all clients within the same IDE (helped me a lot)
• makes tests more flexible as one can inspect/patch methods and attributes while testing

Downsides:

• tests do not reproduce fully realistic scenarios, where each component is an executable (to an extent this is also true for the regtest tests where only a single bitcoind is used)
• it is not clear whether all side effects (state in imported modules) are reset (the order of resetting matters also)

• LN transports are not closed properly -> use a new port (~hacky)
• continue other tests after failed test
• reset side effects in imported modules (need to do more probably)
• synchronization of tests