perf: use a formatter for output
We use a `formatter` object in the perf extensions. This allow the use of
formatted output like json. To avoid adding logic to create a formatter and pass
it around to the timer function in every command, we add a `gettimer` function
in charge of returning a `timer` function as simple as before but embedding an
appropriate formatter.
This new `gettimer` function also return the formatter as it needs to be
explicitly closed at the end of the command.
example output:
$ hg --config ui.formatjson=True perfvolatilesets visible obsolete
[
{
"comb": 0.02,
"count": 126,
"sys": 0.0,
"title": "obsolete",
"user": 0.02,
"wall": 0.0199398994446
},
{
"comb": 0.02,
"count": 117,
"sys": 0.0,
"title": "visible",
"user": 0.02,
"wall": 0.0250301361084
}
]
Hello, Foobar
['Hello, Fo, =;o', 'Hello, Bar']