This patch introduces two tests:

1. `couple.test_failover` reproduces heatbeat timeout on a follower
   that leads to a new election.

2. `threesome.test_leader_dispuption` simulates disconnected follower.
   It shouldn't disrupt the leader in this case.

Leader death is already tested in `threesome.test_log_rollback`.

Close https://gitlab.com/picodata/picodata/picodata/-/issues/25

Also, fix the code to pass the test:

1. Use `replace` instead of `insert` when appending entries. They may be
   overridden.
2. Increase pool worker queue size. Raft node may send several messages
   within a single tick. Without this change the second message is
   dropped.

The second change is a poorly designed workaround. Constant limit
doesn't seem to be both cost-effective and reliable at the same time,
but we don't have a better solution at the moment.

Close https://gitlab.com/picodata/picodata/picodata/-/issues/26

Follower makes a proposal. It's applied on both instances.

This patch also introduces a new API `picolib.raft_status`.

Close https://gitlab.com/picodata/picodata/picodata/-/issues/24

+ tarantool-sys submodule
+ tarantool-patches directory
+ build.rs build script to patch and build tarantool
+ static linking with tarantool
+ refactoring for cli arguments

Close https://gitlab.com/picodata/picodata/picodata/-/issues/23