feat(ParseConfig): Add record + Parse(config) overload (additive)

[dimension-zero]

feat(ParseConfig): Add record + Parse(config) overload (additive)

• ArgumentParser.fs: Introduce public ParseConfig record carrying
  Inputs, ConfigurationReader, IgnoreMissing, IgnoreUnrecognized,
  RaiseOnUsage. Provide ParseConfig.Default reproducing the historical
  Parse(...) defaults.
• New Parse(config: ParseConfig) overload delegates to the existing
  Parse(?inputs, ?configurationReader, ...) implementation. All current
  overloads remain untouched, so existing callers see no shape change.

Useful when hosts want to layer configuration programmatically (e.g.
merging container-provided defaults with user overrides) rather than
juggling many optional method arguments.

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test(ParseConfig): Add coverage for ParseConfig record + Parse(config)

6 new tests:

• ParseConfig.Default holds the historical defaults (None inputs, None
  reader, false IgnoreMissing/IgnoreUnrecognized, true RaiseOnUsage).
• Parse(config with explicit inputs) parses those inputs.
• Parse(config) matches Parse(?inputs, ...) for the same shape.
• IgnoreMissing=true skips the mandatory check on empty inputs.
• IgnoreUnrecognized=true gathers unknown args into UnrecognizedCliParams.
• ConfigurationReader provided via config sources AppSettings entries.

A separate non-mandatory schema is used for the AppSettings test because
Argu's missing-mandatory check fires from CLI parsing even when AppSettings
provides a value (existing behaviour, not introduced by PR 19).

Net suite size on this branch: 112 -> 118.

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[Copilot]

Pull request overview

Adds an additive ParseConfig record and a new Parse(config: ParseConfig) overload on ArgumentParser<'Template> that simply forwards to the existing optional-argument Parse overload. Intended for callers that prefer to assemble parse parameters as data (e.g. layering host defaults over user overrides) rather than through many optional method arguments. Existing overloads are untouched, so this is non-breaking.

Changes:

• Introduce public ParseConfig record (with Default matching historical Parse defaults) in the Argu namespace.
• Add ArgumentParser<'Template>.Parse(config: ParseConfig) overload that delegates to the existing optional-argument Parse.
• Add a new ParseConfigTests.fs covering defaults, explicit inputs, parity with the optional overload, IgnoreMissing, IgnoreUnrecognized, and ConfigurationReader.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/Argu/ArgumentParser.fs	Adds ParseConfig record + Default and a new Parse(config) overload forwarding to existing Parse.
tests/Argu.Tests/ParseConfigTests.fs	New xUnit/Unquote tests for the ParseConfig record and Parse(config) overload.

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[bartelink]

@dimension-zero See #317 (comment) #317 (comment)

I feel it'd be a net win to take ParseConfig out of the picture now (i.e. revert this PR) and focus instead on the extensions layering and rationalizing the top level ParseCommand vs ParseWith(argv, configReader) vs ParseWithAsync(argv, asyncConfigReader) split

All going well, that clarifies matters to the extent that this becomes entirely superfluous