More fixes

[julienblin-kothar]

This PR is for increasing the capabilities offered with REST VOL.

The main thing is really to fix the variable-string read to right-trim all the \0 characters.

The rest is a series of fixes and an overall of the unit tests so that:

• in CI, without REST VOL, everything should pass
• inside the devcontainer, with REST VOL, everything should pass as well - it is just that some tests are OK with being bypassed because REST VOL do not support it correctly.

[vincentmr]

Love this, much cleaner now. I left a couple nitpick suggestions to clean up the code. I think there is only one place where CHECKs were removed and wondering why. Happy to approve afterwards.