Correctly handle dircache for recursive `ls` calls

[AdrianoKF]

The previous implementation of ls would only update the dircache for a single directory, based on the order of info entries returned from the API.

The new implementation correctly adds all directory entries to the dircache, and makes sure that the responses returned from the cache correctly honor the recursive flag.

Closes #200

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (4c647ab) 90.05% compared to head (c1af709) 90.39%. Report is 6 commits behind head on main.

Files	Patch %	Lines
src/lakefs_spec/spec.py	95.34%	0 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #224 +/- ## ========================================== + Coverage 90.05% 90.39% +0.34% ========================================== Files 7 7 Lines 533 552 +19 Branches 85 95 +10 ========================================== + Hits 480 499 +19 Misses 27 27 Partials 26 26 ```

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