Add rsrv logger for machine topology

[elliottslaughter]

Fixes #458.

Adds a new -level rsrv=2 logger that replaces -ll:show_rsrv. Right now the old code paths are still in place, and this new code path works independently of the old flag. Use -level rsrv=2 OR -ll:show_rsrv, not both.

Alternatives/design decisions:

• We could remove -ll:show_rsrv in favor of the new logger, possibly with an error message to users who attempt to use it, directing to the new syntax.
• The logger currently prefixes only the first line, because we reuse the existing infrastructure for printing to a stream. If we wanted every line to be prefixed, we'd need to make deeper changes.

Output looks like:

$ ./examples/saxpy/saxpy -level rsrv=2
[0 - 1fb2b5e80]    0.000126 {2}{rsrv}: Topology {
  domain 0, memory size:68719476736 {
    core 0 { ids=<0> }
    core 1 { ids=<1> }
    core 2 { ids=<2> }
    core 3 { ids=<3> }
    core 4 { ids=<4> }
    core 5 { ids=<5> }
    core 6 { ids=<6> }
    core 7 { ids=<7> }
    core 8 { ids=<8> }
    core 9 { ids=<9> }
    core 10 { ids=<10> }
    core 11 { ids=<11> }
    core 12 { ids=<12> }
    core 13 { ids=<13> }
    core 14 { ids=<14> }
    core 15 { ids=<15> }
    core 16 { ids=<16> }
    core 17 { ids=<17> }
  }
}
CPU proc 1d00000000000001: allocated <0>
dedicated worker (generic) #1: allocated <1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17>
dedicated worker (generic) #2: allocated <1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17>
utility proc 1d00000000000000: allocated <1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17>

[codecov]

Codecov Report

❌ Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.
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✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/realm/runtime_impl.cc	0.00%	7 Missing ⚠️

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[lightsighter]

Can we name it core_rsrv or something along those lines to avoid conflating it with actual Realm reservations and their loggers? I would be in favor of just removing the old flag to avoid building up cruft, but open to alternative opinions on that front. I don't think anyone keys off of -ll:show_rsrv enough to keep it around.