chore(deps): bump leanMultisig (5eba3b1) and leansig (c08a3ba) (lambdaclass#387)

## Summary
- Bumps `leanMultisig` (`lean-multisig`, `leansig_wrapper`) from
`2eb4b9d` to `5eba3b1` (latest `devnet4`).
- Bumps `leansig` to `c08a3ba` by following its default branch.
`leanMultisig` depends on `leansig` without a `branch`/`rev` spec, so
matching that source avoids two `leansig` copies in `Cargo.lock`.
- Adapts to the upstream rename
`SchemeAbortingTargetSumLifetime32Dim46Base8` →
`SIGAbortingTargetSumLifetime32Dim46Base8` in
`crates/common/types/src/signature.rs`.

## Test plan
- [ ] `make lint`
- [ ] `make test`
- [ ] Smoke-test on a local devnet (`make run-devnet`)

Author: MegaRedHand