Remove prctl dependency that is not available on mac.

feat: raft peer discovery PoC

chore: prevent C functions from being optimized out

feat: improve peer discovery

fix: fix tests after making instance_id arg mandatory

Smart supevision with fork

Make it work

Under development

IPC messages to supervisor

One more little step: entrypoint enum

Arrange IPC from child to supervisor

Remove tarantool_main macro

Persist snapshot

Fix some fresh bugs

Implement postjoin

Discovery under refactoring

Enhance discovery

Working on discovery

Fix all discovery bugs known so far

Draft join algorithm

Fail applying snapshot

Joining a learner works

Cleanup snapshot generation

Reorganize traft code and call join automatically

Change peer.commit_index type from option to u64

Implement autopromotion to voter

Implement read_index

Take read_index before self-romotion

Cleanup excess logs

Cleanup logs and code

Deep refactoring in progress

Finish refactoring db schema

Embed entries applying inside traft node

Refactor raft node communication

Replace fiber channel with a mailbox, which is a `Vec<_>` + fiber cond.
It allows to batch raft commands in a more predictable way and makes
the code less error-prone.

Remove commented code

Simplify raft nodes interaction over net_box

Eliminate `traft::Message` struct because its internals aren't used.
Instead, serialize `raft::Message` using protobuf.

Batch ConnectionPool requests

1. Send messages in batches.
2. Allow changing connection uri.
3. Close unused connections after `inactivity_timeout`.

Enhance the raft node

1. Collect results from raft node
2. Fix initial bootstrap which used to fail due to fiber race.
3. Wrap raft storage operations in a transaction.

Bump tarantool module

Add documentation draft

Cleanup warnings

Try fixing tests

Fix test_storage_log

Fix test_traft_pool

Fix luatest single and couple

Start fixing threesome test

Implement concurrent join requests handling

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

Module `traft::storage` doesn't panic anymore. Instead, it gracefully
returns errors. All unwraps are moved to the calling functions.

Also, the code is supplemented by tests, and debug logs are removed.

1. Replace `From` trait for raft::Entry with the `TryFrom`. Fairly
   handle its errors in the storage.

2. Replace some other unwraps with "expect" with a more clear message.

3. Support all of `raft::EntryType` variants.

Tarantool specificities make it difficult to set up usual rust tests.
Picolib is coupled with tarantool symbols and compiled as a dylib, so
it can't be linked to a stand-alone binary.

This patch introduces another way of testing.

All tests (called inner) are already built into dylib and exposed in
the tarantool console:

```
tarantool> picolib.test
---
- test_version: 'function: 0x41f32400'
  test_traft_storage_RaftEntryRow: 'function: 0x41f32550'
...
```

The new integration test `inner.rs` iterates over them and runs each
one in a separate tarantool instance.

See also: commit 6610e5cb

Close https://gitlab.com/picodata/picodata/picodata/-/issues/10

- There's a fiber which ticks logical clock.
- There's a `raft_propose` API exposed in the Tarantool console.

Close https://gitlab.com/picodata/picodata/picodata/-/issues/7
Close https://gitlab.com/picodata/picodata/picodata/-/issues/8

It used to panic if the env variable wasn't set.
Also, this patch covers it with tests.

The control flow of picodata looks as following:

Picodata binary -> exec tarantool -l picodata -> libpicodata.so -> ...

Since the libpicodata is a shared lib loaded by tarantool, we can't pass
it arguments as usual. At first, tarantool parses them by itself and
rejects uknown arguments. Secondly, it spoils argv array.

To overcome these two issues, this patch introduces argparse on behalf
of the picodata binary, and puts parsed values into the environment
variables.

P.S. Thihs is how command line args look from within libpicodata:

```console
$ tarantool -l picodata /dev/null --opt1 foo --opt2 bar
Hello from rust lib
arg[0] tarantool
arg[1] /dev/null
arg[2] --opt1
arg[3] foo
arg[4] --opt2
arg[5] bar
arg[6] --opt2
arg[7] bar
```

This patch introduces the new cargo package - picodata.

The package consists of two parts:
- The `picodata` binary does some env magic and executes
  `tarantool -l picodata`.
- The `libpicodata` dylib is the starting point for further
  development.