[MEDIUM] http: rework chunk-size parser

[MEDIUM] http: rework chunk-size parser

Chunked encoding can be slightly more complex than what was implemented.
Specifically, it supports some optional extensions that were not parsed
till now if present, and would have caused an error to be returned.

Also, now we enforce check for too large values in chunk sizes in order
to ensure we never overflow.

Last, we're now able to return a request error if we can't read the
chunk size because the buffer is already full.