fix #6881 - add policies for too long ids from a str and use short as default

[RonnyPfannschmidt]

this experiments with addign a policy and a new default

• short(default) - if the str is longer than 100, use the normal shorten
• hash: make a sha256 of the value
• legacy: just take the long str, for transitons
• disallow: juexpect people to pick ids

closes #6881

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

src/_pytest/python.py:114

• Typo 'parameer' should be 'parameter', and the help text mentions 'sha3' while the code uses hashlib.sha256. Please update for consistency.

        help="strategy for parameer values that result in long ids\n- short: default: shorten the value normally\n- hash: take a sha3 of the value for content matching ids\n- legacy: keep the long id (only use this for temporary backward compatibility)\n- disallow: fail and request explicit ids",

testing/python/metafunc.py:666

• [nitpick] The expected output for the 'short' strategy ('a0') when the input string is long is non-obvious. Please add a comment to clarify the rationale for this expected value.

            "short": "a0",