Add `ComputeNode`, `LocalV2` + deprecate `RemoteV1` and `LocalV1`

[lebrice]

What this does

This PR adds some new functions and classes which will be used in the near future to significantly refactor most commands of milatools.

Once these commands are made to use the content of this PR, they will:

• Properly support ssh keys with a passphrase
• Properly support clusters where 2FA is enabled (only goes through 2FA once)
• Resolve all paramiko issues
• Greatly reduce the connection latency for all commands that connect to the mila cluster (such as mila code).

Highlights for reviewers (take a look at this first):

I would appreciate it if you could take a quick look at a few particular things, if you feel like it of course:

• LocalV2
  • the run function: https://github.com/lebrice/milatools/blob/add_computenode_localv2/milatools/utils/local_v2.py#L102
  • the run_async function: https://github.com/lebrice/milatools/blob/add_computenode_localv2/milatools/utils/local_v2.py#L102
• ComputeNode
  • the salloc function: https://github.com/lebrice/milatools/blob/add_computenode_localv2/milatools/utils/compute_node.py#L278
  • the sbatch function: https://github.com/lebrice/milatools/blob/add_computenode_localv2/milatools/utils/compute_node.py#L359
  • the ComputeNode.run method : https://github.com/lebrice/milatools/blob/add_computenode_localv2/milatools/utils/compute_node.py#L69

Here's a little class diagram illustrating the relationship between Runner, LocalV2, RemoteV2, and ComputeNode:

classDiagram
direction BT
class Runner
<<abstract>> Runner
class Runner{
    str hostname
    run(command) CompletedProcess
    run_async(command) CompletedProcess
    get_output(command) str
    get_output_async(command) str
}

LocalV2 --|> Runner : implements

class RemoteV2 {
    LocalV2 local_runner
    async connect(hostname) RemoteV2
}
RemoteV2 --|> Runner : implements

class ComputeNode {
    RemoteV2 login_node
    int job_id
    close()
}
ComputeNode --|> Runner : implements

Refactor:

• Adds RemoteV2.connect, an asynchronous constructor for connecting to a cluster;
• Adds async salloc and sbatch function that request ressources and return a ComputeNode
• Adds a ComputeNode class that can be used to run commands inside a job.
• Deprecate the use of LocalV1, RemoteV1 and SlurmRemote: Code editors will show that using these is now discouraged. Importantly, this will NOT raise a warning to the user.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.25478% with 93 lines in your changes are missing coverage. Please review.

Project coverage is 62.21%. Comparing base (ce86eae) to head (212658b).

Files	Patch %	Lines
milatools/utils/compute_node.py	67.82%	65 Missing :warning:
milatools/utils/remote_v2.py	88.32%	16 Missing :warning:
milatools/cli/commands.py	41.66%	7 Missing :warning:
milatools/utils/local_v2.py	97.70%	2 Missing :warning:
milatools/utils/runner.py	88.23%	2 Missing :warning:
milatools/cli/utils.py	91.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #112 +/- ## ========================================== - Coverage 65.58% 62.21% -3.37% ========================================== Files 12 15 +3 Lines 1781 2178 +397 ========================================== + Hits 1168 1355 +187 - Misses 613 823 +210 ``` | [Flag](https://app.codecov.io/gh/mila-iqia/milatools/pull/112/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | Coverage Δ | | |---|---|---| | [integrationtests](https://app.codecov.io/gh/mila-iqia/milatools/pull/112/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | `62.21% <80.25%> (-3.37%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia#carryforward-flags-in-the-pull-request-comment) to find out more.

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[lebrice]

I will rebase this and make it much cleaner and easier for others to review. I'll mark this as "ready for review" when I'm done. Should probably be done today.