dulwich: support interactive SSH key passphrase prompt in asyncssh vendor

[pmrowla]

Closes iterative/dvc#9737

• Makes scmrepo behave the same as git when prompting for a passphrase

$ dvc import git@github.com:pmrowla/test-dvc-private.git data/data.xml
Importing 'data/data.xml (git@github.com:pmrowla/test-dvc-private.git)' -> 'data.xml'
Cloning test-dvc-private.git|                             |0.00/? [00:00,      ?obj/s]
Enter passphrase for key '~/git/scratch/test-ssh-passphrase/id_ed25519':

To track the changes with git, run:

        git add data.xml.dvc

To enable auto staging, run:

        dvc config core.autostage true

[pmrowla]

We should also probably consider using a similar InteractiveSSHClient implementation in dvc-ssh instead of using the current ask_password/ask_passphrase options (which require the user to use those remote flags and prompt before we try to make any SSH connection or try any specific SSH keys)

related: iterative/dvc-ssh#3

[codecov-commenter]

Codecov Report

Patch coverage: 30.90% and project coverage change: -0.67 ⚠️

Comparison is base (c29edf7) 80.98% compared to head (4980cba) 80.31%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #255      +/-   ##
==========================================
- Coverage   80.98%   80.31%   -0.67%     
==========================================
  Files          27       27              
  Lines        4059     4114      +55     
  Branches      719      727       +8     
==========================================
+ Hits         3287     3304      +17     
- Misses        647      681      +34     
- Partials      125      129       +4     

Impacted Files	Coverage Δ
src/scmrepo/git/backend/dulwich/asyncssh_vendor.py	61.32% <30.90%> (-13.28%)	⬇️

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[pmrowla]

On the scmrepo side, some of this could also be generalized a bit more and re-used in git.credentials to implement full support for SSH auth in pygit2/libgit2 (which will require loading keys via asyncssh and then passing them into the pygit2 credential callbacks), but that can be done in a follow-up PR if/when needed

[efiop]

Good to know there is a way to detect key errors with asyncssh. That ask_pass stuff is from paramiko days, where it didn't have that mechanism.