[tracer] limit span and trace IDs to 63 bits

[ufoot]

One note here: I changed the MAX_ID to be 2**63 and not 2**63 -1 because most of the code using it needs the upper "excluded" limit. Eg, rand(2) returns 0 or 1, never 2. Also, we use operator % and it's the same -> to get something between 0 and MAX_ID, including MAX_ID, you'd do n % (MAX_ID+1). Globally, code is simpler when MAX_ID is just plain 2**63 without the - 1.

[palazzem]

Perfect! I'll be sure that this happens also to the Python client. Thank you!