Close banks to recover rent

[jgur-psyops]

Provided a bank has no outstanding deposits, loans, or collected fees, add an ix to close a bank to recover the account rent.

[0xathletic]

@jgur-psyops would you share more details on this issue?
any materials or code files to kick off ...

[jgur-psyops]

@jgur-psyops would you share more details on this issue? any materials or code files to kick off ...

some Integrators have asked for a command similar to account closure https://github.com/mrgnlabs/marginfi-v2/blob/main/programs/marginfi/src/instructions/marginfi_account/close.rs

for defunct banks that no longer have any assets or banks created by accident. We want to avoid allowing banks to be closed if they have any participating users in any way, for example a bank might have zero assets but still owe some emissions, in which case it should stay live, so there are some edge cases here. A MWE can support just banks created in the future.

This is relatively low priority because the associated rent is not that much.