Fix to Producer Busy error on reconnect

[CMoore-Darwinium]

Hi, this is a fix for this issue, that we've been getting:
apache/pulsar#13342

It's a direct clone of this Go fix, which is why it uses an atomic int even though it doesn't really need to:
https://github.com/apache/pulsar-client-go/pull/582/files

[tisonkun]

Please run cargo +nightly fmt --all locally to fix the style issue.

I'd like to help you but your branch name conflict with upstream so it's hard to directly push on your changes.

➜  pulsar-rs git:(darwinium-com/master) git push
fatal: The upstream branch of your current branch does not match
the name of your current branch.  To push to the upstream branch
on the remote, use

    git push origin HEAD:refs/pull/280/head

To push to the branch of the same name on the remote, use

    git push origin HEAD

To choose either option permanently, see push.default in 'git help config'.

To avoid automatically configuring an upstream branch when its name
won't match the local branch, see option 'simple' of branch.autoSetupMerge
in 'git help config'.

➜  pulsar-rs git:(darwinium-com/master) git push origin HEAD:refs/pull/280/head
Enumerating objects: 34, done.
Counting objects: 100% (31/31), done.
Delta compression using up to 10 threads
Compressing objects: 100% (24/24), done.
Writing objects: 100% (24/24), 4.15 KiB | 4.15 MiB/s, done.
Total 24 (delta 19), reused 0 (delta 0), pack-reused 0
remote: Resolving deltas: 100% (19/19), completed with 6 local objects.
To https://github.com/streamnative/pulsar-rs.git
 ! [remote rejected] HEAD -> refs/pull/280/head (deny updating a hidden ref)
error: failed to push some refs to 'https://github.com/streamnative/pulsar-rs.git'

[tisonkun]

Besides, can you pick the test cases in Golang patch also so that we can prevent regression later?