Improve unit-test coverage on old and/or pure-ish functions/modules in src/or
These files have the most old code in src/or right now, and they have a lot of functions that are mostly pure-ish functions. Let's call these low-hanging fruit.
routerparse.c.gcov 717 1620 69.32
routerlist.c.gcov 1496 588 28.21
nodelist.c.gcov 503 165 24.70
rendcache.c.gcov 332 1 0.30
networkstatus.c.gcov 681 144 17.45
policies.c.gcov 244 506 67.47
rephist.c.gcov 931 278 22.99
buffers.c.gcov 361 506 58.36