ENH: Add analysis of single results

[HaoZeke]

Closes #370, #1452. Related to #789 but without leaning into the requirement of having to use asv's environment management.

This is still a WIP, clearly it needs to be folded into the Command pattern used throughout ASV (or pending a full switch to click).

[HaoZeke]

Looks a bit like this:

python ../asv/comparer_bench.py .asv/results/rgx1gen11/a0f29428-conda-py3.11.json .asv/results/rgx1gen11/a0f29428-conda-py3.11-numpy.json .asv/results/benchmarks.json
Hello, comparing .asv/results/rgx1gen11/a0f29428-conda-py3.11.json and .asv/results/rgx1gen11/a0f29428-conda-py3.11-numpy.json!

All benchmarks:

| Change   | Before     | After     |   Ratio | Benchmark (Parameter)   |
|----------|------------|-----------|---------|-------------------------|
| +        | 34.0±0.1μs | 94.8±30μs |    2.79 | b [e]                   |

• Technically benchmark.json is only used to get units which aren't reported (here) but probably should be.
• The naming should be user defined, parameters need to work
• Warning on very different samples

[HaoZeke]

Closing in favor of the https://github.com/HaoZeke/asv_spyglass repo where changes can be tracked better.