session: Improvements and test coverage

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 73.33333% with 28 lines in your changes missing coverage. Please review.

Project coverage is 54.21%. Comparing base (ab1e38b) to head (82cdd36). Report is 26 commits behind head on master.

Files with missing lines	Patch %	Lines
client/container.go	28.57%	12 Missing and 3 partials :warning:
crypto/signature.go	75.00%	7 Missing :warning:
bearer/bearer.go	64.70%	5 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #612 +/- ## ========================================== + Coverage 53.93% 54.21% +0.27% ========================================== Files 164 164 Lines 19222 19191 -31 ========================================== + Hits 10368 10405 +37 + Misses 8415 8358 -57 + Partials 439 428 -11 ```

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[cthulhu-rider]

reverted all interface changes (deprecations) except several extensions which i consider very valuable since they are based on real NeoFS dev experience. The only element that I still abolish is StaticSigner. Again, according to devX, it is quite incomprehensible. Now that you can easily create and insert ready-made signatures, fake signer becomes absolutely unnecessary

i need a bit more time to fix tests which were based on API which did not justify itself