Loan manager deposit collateral cei fix

[jotel-dev]

I added a regression test that installs a malicious token contract which removes the loan during transfer
verifies deposit_collateral returns Err(LoanError::LoanNotFound) safely
Next:

closes #17

[ogazboiz]

nice work on this one. the core restructuring is exactly right: you commit the updated collateral to storage before the token transfer and replaced every expect with a typed error, so it now matches the cei pattern used in repay and approve_loan. the malicious-token regression test is a great touch and the assertion (Err(LoanError::LoanNotFound)) lines up with the re-read path.

that said, the pr currently does not compile, so i cannot merge it yet. a few asks:

1. loan_manager/src/lib.rs:1356 - let loan: Loan needs to be let mut loan: Loan. line 1390 mutates loan.collateral_amount, so the build fails with E0594 (cannot assign, not declared as mutable).

2. multisig_governance/src/test.rs:5-6 - the //! inner doc comment sits after a use statement, which rust rejects (E0753). switch those two lines to regular // comments.

3. run cargo fmt - the new import line in loan_manager/src/test.rs:3 needs to be split across lines to pass cargo fmt --check.

4. the multisig_governance changes (count_valid_approvals plus its test) look like they came in from a different branch. could you rebase onto main so this pr only contains the deposit_collateral fix? that keeps it scoped to issue #17 and is what introduces the E0753 above.

one small optional note: the event at lib.rs:1407 still publishes the pre-transfer loan fields rather than the re-read stored_loan. it is harmless since state is already durable before the transfer, just flagging it.

once it compiles and cargo fmt/clippy/test are green, this should be good to go. the logic itself is solid.

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