Add nnbench compare subcommand, comparison function

[nicholasjng]

Works using metric (benchmark) names as columns, and records as lines. Alternatively, we could support metrics as rows and record IDs as columns in the future.

Contains logic to add parameter values and context values to the table as columns, also directly on the command line. In the future, we could make a comparison class that can be subclassed to avoid option clutter on the command line for customizing the rich table display.

[nicholasjng]

Works on regular records:

nnbench compare rec1.json rec2.json -P a -P b -C foo
┏━━━━━┳━━━━━┳━━━━━━━━━━━┳━━━━━━━━━━━┳━━━━━┓
┃ add ┃ mul ┃ Params->a ┃ Params->b ┃ foo ┃
┡━━━━━╇━━━━━╇━━━━━━━━━━━╇━━━━━━━━━━━╇━━━━━┩
│ 3   │ 2   │ 1         │ 2         │ baz │
│ 4   │ 3   │ 1         │ 3         │ baz │
└─────┴─────┴───────────┴───────────┴─────┘

as well as on records with benchmarks containing errors (example: a sub function throwing an "unsupported" error):

┏━━━━━┳━━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━┳━━━━━━━━━━━┳━━━━━┓
┃ add ┃ mul ┃ sub                       ┃ Params->a ┃ Params->b ┃ foo ┃
┡━━━━━╇━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━╇━━━━━━━━━━━╇━━━━━┩
│ 3   │ 2   │ ERROR: sub is unsupported │ 1         │ 2         │ bar │
│ 4   │ 3   │ -----                     │ 1         │ 3         │ baz │
└─────┴─────┴───────────────────────────┴───────────┴───────────┴─────┘

[nicholasjng]

Merging this now, the (numerous) follow-ups can be tackled in other issues, but don't have to be implemented for the next release yet.