Move minimum boost version to 1.59

Summary:
Debian stable ships with 1.67 and Ubuntu LTS with 1.65

This will simplify the use of timeouts for tests.

Test Plan:

ninja all check
make check

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6762