Document robots.txt support, and let run_script pass browser flags

[arrufat]

The browser has had --obey-robots since before these bindings existed, and
nothing here mentioned it, so nobody using the package would find it. It is now
a README section and appears in the pdoc reference, on the landing page and on
each class that takes args=.

Most of that section is spent on the part that surprises people, verified
against a live site rather than assumed: the rule applies to every request,
not just the page you asked for. Sites commonly disallow the directory their own
assets live in, so a permitted page can load with its scripts blocked and render
blank. On neurips.cc — the site examples/neurips_topics.py reads — the page
is allowed but its JavaScript sits under /static, which their robots.txt
disallows, so the paper list never appears. That is robots.txt working, and
without saying so the obvious conclusion is that the flag is broken.

run_script was the one entry point that could not enable it, taking no flags at
all. It and run_script_async now accept args= like everything else, with a
test that passes a flag the binary rejects, so it needs no network.

Not added: a named obey_robots= parameter. Every other browser flag goes
through args=, and promoting one creates a second way to say the same thing
plus a conflict to resolve when both are passed.

The second commit is unrelated and can be dropped if you would rather it landed
separately: rebuilding the pdoc docs regenerates _methods.py, which was stale.
The browser gained regex matching for findElement's name argument and the
regenerated docstring never landed here. That change is in the browser's main,
so nightly has it and CI would have failed on the next push regardless.