stretch goals: Introduce Session-based Request Distribution

[zvolin]

No description provided.

[oblique]

Session needs to handle partial range responses: #67 (comment)

[oblique]

Since partial responses are allowed:

• Here we should return the error only if vector is empty.
• Here in case of failure if some headers passed verification, we should return them instead of an error.

Session should retry requesting the remaining range.

[oblique]

We need to figure out this: Should requests that failed because of a connection error be retried?