perf(markers): speed up _format_marker and benchmark str(Marker)

[notatallshaw]

_format_marker backs str(Marker), and through it Marker.__hash__, Marker.__eq__ and Requirement.__str__.

	before	after
marker item	" ".join([m.serialize() for m in marker])	f"{lhs.serialize()} {op.serialize()} {rhs.serialize()}"
isinstance(marker, list)	twice, guard then dispatch	once, with the guard folded in
(list, tuple, str), (list, tuple)	rebuilt per call	module constants
inner	(_format_marker(m, first=False) for m in marker)	[_format_marker(m, first=False) for m in marker]

A marker item is always (Variable | Value, Op, Variable | Value), so the comprehension and the join are avoidable.

_format_marker takes about 0.75x the time it did, on CPython 3.10, 3.12, 3.14 and 3.15.

TimeMarkerSuite timed the constructor and evaluate but not str, so ASV had no view of this path. time_str adds one.

I started looking at this while reading #1370.

[notatallshaw]

Faster:

| Change   | Before [ef91ddbe]    | After [c4b433f9]    |   Ratio | Benchmark (Parameter)                                                                                  |
|----------|----------------------|---------------------|---------|--------------------------------------------------------------------------------------------------------|
|          | 5.48±0.03ms          | 5.46±0.03ms         |    1    | markers.TimeMarkerSuite.time_constructor [runnervmvrwv9/virtualenv-py3.10-PYTHONHASHSEED0]             |
|          | 4.06±0.03ms          | 4.05±0.02ms         |    1    | markers.TimeMarkerSuite.time_constructor [runnervmvrwv9/virtualenv-py3.11-PYTHONHASHSEED0]             |
|          | 4.66±0.04ms          | 4.69±0.03ms         |    1.01 | markers.TimeMarkerSuite.time_constructor [runnervmvrwv9/virtualenv-py3.12-PYTHONHASHSEED0]             |
|          | 4.69±0.03ms          | 4.69±0.02ms         |    1    | markers.TimeMarkerSuite.time_constructor [runnervmvrwv9/virtualenv-py3.13-PYTHONHASHSEED0]             |
|          | 4.56±0.04ms          | 4.58±0.03ms         |    1.01 | markers.TimeMarkerSuite.time_constructor [runnervmvrwv9/virtualenv-py3.14-PYTHONHASHSEED0]             |
|          | 1.07±0.01ms          | 1.09±0.01ms         |    1.01 | markers.TimeMarkerSuite.time_evaluate [runnervmvrwv9/virtualenv-py3.10-PYTHONHASHSEED0]                |
|          | 749±6μs              | 749±7μs             |    1    | markers.TimeMarkerSuite.time_evaluate [runnervmvrwv9/virtualenv-py3.11-PYTHONHASHSEED0]                |
|          | 879±2μs              | 880±7μs             |    1    | markers.TimeMarkerSuite.time_evaluate [runnervmvrwv9/virtualenv-py3.12-PYTHONHASHSEED0]                |
|          | 826±8μs              | 827±6μs             |    1    | markers.TimeMarkerSuite.time_evaluate [runnervmvrwv9/virtualenv-py3.13-PYTHONHASHSEED0]                |
|          | 783±4μs              | 774±20μs            |    0.99 | markers.TimeMarkerSuite.time_evaluate [runnervmvrwv9/virtualenv-py3.14-PYTHONHASHSEED0]                |
| -        | 542±5μs              | 388±7μs             |    0.72 | markers.TimeMarkerSuite.time_str [runnervmvrwv9/virtualenv-py3.10-PYTHONHASHSEED0]                     |
| -        | 373±8μs              | 246±5μs             |    0.66 | markers.TimeMarkerSuite.time_str [runnervmvrwv9/virtualenv-py3.11-PYTHONHASHSEED0]                     |
| -        | 407±30μs             | 293±9μs             |    0.72 | markers.TimeMarkerSuite.time_str [runnervmvrwv9/virtualenv-py3.12-PYTHONHASHSEED0]                     |
| -        | 392±8μs              | 272±4μs             |    0.69 | markers.TimeMarkerSuite.time_str [runnervmvrwv9/virtualenv-py3.13-PYTHONHASHSEED0]                     |
| -        | 401±7μs              | 289±3μs             |    0.72 | markers.TimeMarkerSuite.time_str [runnervmvrwv9/virtualenv-py3.14-PYTHONHASHSEED0]                     |

[henryiii]

By the way, here or as a followup, we could do #1252 on Marker, which would cut the repeated __hash__ time down. Marker is currently fully immutable. (Specifiers have one mutable property, and Requirements are mutable currently).

[notatallshaw]

Specifiers have one mutable property

As a complete aside, I've been thinking of adding a class method calls with_prerelease that allows you to get a new specifier with the prerelease of your choice, and then deprecating the mutability of the prerelease property, not sure what the timeline of that should look like though.

[henryiii]

What about supporting __replace__ instead?

[henryiii]

All benchmarks:

Change	Before [ef91ddb]	After [cd3b319]	Ratio	Benchmark (Parameter)
-	528±5μs	370±5μs	0.7	markers.TimeMarkerSuite.time_str [runnervmvrwv9/virtualenv-py3.10-PYTHONHASHSEED0]
-	359±10μs	222±4μs	0.62	markers.TimeMarkerSuite.time_str [runnervmvrwv9/virtualenv-py3.11-PYTHONHASHSEED0]
-	384±8μs	252±6μs	0.66	markers.TimeMarkerSuite.time_str [runnervmvrwv9/virtualenv-py3.12-PYTHONHASHSEED0]
-	373±7μs	252±4μs	0.68	markers.TimeMarkerSuite.time_str [runnervmvrwv9/virtualenv-py3.13-PYTHONHASHSEED0]
-	385±5μs	267±3μs	0.7	markers.TimeMarkerSuite.time_str [runnervmvrwv9/virtualenv-py3.14-PYTHONHASHSEED0]