feat(validation): add In<T> and InList<T extends Enum> whitelist rules

[anilcancakir]

Closes #81

Summary

Adds two Laravel-style whitelist rules to the validation system:

• In<T>(List<T> values) — primitive whitelist. The generic T makes type mismatches fail explicitly instead of silently coercing.
• InList<T extends Enum>(values, {caseInsensitive, wire}) — enum-aware variant. Accepts the enum instance itself or a string compared against Enum.name. Pass wire: to map enums onto snake_case or bespoke wire codes, caseInsensitive: true for loose string matching.

Both rules short-circuit on null (pair with Required() for presence) and emit the shared validation.in message with a comma-joined :values placeholder.

'visibility': [In<String>(['public', 'private'])],
'priority':   [In<int>([1, 2, 3, 5, 8])],
'severity':   [InList(Severity.values)],
'direction':  [InList(ThresholdDirection.values,
                wire: (d) => d == ThresholdDirection.highBad ? 'high_bad' : 'low_bad')],

Test plan

• 21 new tests in test/validation/in_rule_test.dart covering both rules (type guards, null short-circuit, Validator integration, wire/caseInsensitive combos, params exposure)
• flutter test — all 1019 tests green
• dart analyze — zero warnings
• dart format — clean
• CHANGELOG [Unreleased] updated
• doc/digging-deeper/validation.md — new Whitelist Rules section
• skills/magic-framework/references/forms-validation.md — rule table + gotcha

[sentry]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[Copilot]

Pull request overview

Adds Laravel-style whitelist validation rules to Magic’s validation system, including a typed primitive whitelist and an enum-aware variant.

Changes:

• Introduces new In<T> and InList<T extends Enum> validation rules with validation.in messaging + :values params.
• Exports the new rules via lib/magic.dart and documents usage in framework docs/reference material.
• Adds a dedicated test suite validating rule behavior and Validator integration.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
lib/src/validation/rules/in_rule.dart	Implements In<T> and InList<T extends Enum> rules and their message params.
lib/magic.dart	Exposes the new rule(s) through the public barrel export.
test/validation/in_rule_test.dart	Adds end-to-end and unit tests for both whitelist rules.
doc/digging-deeper/validation.md	Documents the new whitelist rules and provides examples.
skills/magic-framework/references/forms-validation.md	Updates the built-in rules reference table and gotchas.
CHANGELOG.md	Notes the new validation rules under Unreleased.