fix: Open the door for adding value_parser! specializations

fix: Further discourage `value_parser!` implementation details

I wanted to make the contract more clear that we might add more specific
value parsers in the fu...

Newstyle flags have defaults which prevents them from being required
until now.

- This matches the more container-like naming we are aiming for
- This provides an opportunity t...

This was missed in #3453

fix(parser): Always include pending arguments in errors

Found via cargo's UI tests

perf(parser): Take up less memory with ArgAction::Count

Someone should not reasonably expect a coun flag to go up to billions,
millions, or even thousan...

docs: Update changelog

fix(builder): Clean up after hiding `AnyValueParser`

There isn't a strong need for the single-instance at the cost of the
extra book keeping.

My hope is this will provide clearer error messages for the user.

With `AnyValueParser` now private, we can also make `AnyValue` private.
Most users should not ne...

fix(assert): Reslve regressions for auto-help / auto-version

Make `AnyValueParser` private

refactor(builder): Reduce visibility

fix(help): Deprecate NoAutoVersion/NoAutoHelp

I'm a bit disappointed we don't have a way to control the action for the
help subcommand. Inste...

fix(derive): Clarify ArgEnum as ValueEnum

We aren't enumerating arguments but values for an argument, so the name
should reflect that.

Th...

docs(tutorial): Update for new API

fix: Deprecate features redundant with Actions

Fixes #3772

For programs opting into the clap v4 behavior (with `action` or
`value_parser` attributes), we'l...

This is needed for deprecate `multiple_occurrences`

This mostly exist for
- Knowing of the value came from the command-line but we now have
`ArgMa...

This shouldn't be needed anymore now that this is effectively the new
behavior for the non-depre...

Dropping these will help simplify a lot, including removing of
occurrences.

These come at the c...

feat(derive): Expose control over Actions

This is the derive support for #3774 (see also #3775, #3777)

This combined with `value_parser` ...

fix(validator): Ignore defaults for requireds

This is a follow up to #3420. Its easy to overlook this because it is only
useful for the condi...

refactor: Prep for actions in derive

Now that flags can have meaningful defaults and with defaults being
implicitly set for certain a...

Originally I hid all, assuming the flag-only use case but we had to
prevent that from showing up...

I thought I had broken this but it always seemed to have worked this way

Unsure why a comment said this doesn't matter. It matters both for
counting arguments and for r...

refactor(bench): Pull out benchmarks into own crate

This is mostly about avoiding criterion's build times when just
developing clap itself.

I'm ass...

fix(parser): Provide default value for Actions

Actions were inspired by Python and Python does not implicitly default
any field when an action ...

refactor(derive): Prepare for action support

This reverts commit 50f4018dcfb1f33cb092780e27f14bfed5b0ed2c.

This broke compatibility with the...

This exposed a potential bug but I figure it isn't worth fixing without
actions.

refactor(derive): Merge handling of bool/from_flag

fix(parser): Don't treat missing values as missing args

This could cause surprising results for users as we add fields

This will make it easier to divide off parser logic for adding in
actions.

This does mean we ca...

docs(builder): Note the type for 'Count'

fix(derive): Align value parser's type with occurrences_of