[rejected AI] Fix count=True ignoring non-zero default

[ShamikOfficial]

When count=True options have a non-zero default, Click previously counted from 0 whenever the flag appeared on the command line. That could produce a value lower than the default (for example default=3 with one -v yielded 1).

This change makes command-line counts additive relative to the option default (and Context.default_map when present), matching argparse action="count".

fixes #3841

• Added parametrized tests for non-zero defaults and a default_map baseline test.
• Documented behavior in the Option docstring (.. versionchanged:: 8.5.1).
• Added a CHANGES.md entry under 8.5.1.

[roli-lpci]

count=True also accepts string defaults, which Click normally converts through
the option's integer type. On this head, the new addition happens before that
conversion, so an explicit count crashes for either default source:

@click.command()
@click.option("-v", count=True, default="3")
def cli(v):
    click.echo(v)

runner.invoke(cli, []).output       # "3\n" (an int in the callback)
runner.invoke(cli, ["-v"]).exception
# TypeError: can only concatenate str (not "int") to str

The same exception occurs with default_map={"v": "3"}. Both baselines are
still raw strings in consume_value, while the parser count is an int; normal
type conversion only runs later in handle_parse_result. Could the baseline be
converted through the option type before adding it, with coverage for string
values from both default and default_map?

[davidism]

https://palletsprojects.com/contributing/llm-ai