Expose exact-target AppInstallManager cancellation

Parent: #232

Dependencies and access restriction

Depends on #233, #234, #236. Implementation remains blocked until the supported-access gate and listed prerequisites are complete.

Microsoft documents AppInstallManager access as protected by a private capability restricted to Microsoft-developed apps. Do not bypass that restriction or treat runFullTrust/admin access alone as sufficient.

API scope

Manager Cancel overloads, with item-level Cancel mapping where needed for exact typed identity.

Acceptance criteria

• Resolve an exact documented product/item target; preserve user and group context and reject ambiguous/disappeared items before acting.
• Confirm cancellation through ShouldProcess, disclosing ItemOperationsMightAffectOtherItems and bundle effects.
• Preserve optional correlation input without hardcoding telemetry identifiers. Do not interpret native void return as proof that the item reached a cancelled terminal state.
• Return an honest request outcome or explicitly observed state; distinguish completion races, access failures and cancellation failures.
• -WhatIf never cancels; no automatic cancellation on inventory or monitor disposal.

Shared delivery requirements

Follow the parent epic's compiled-C# contract, user-scope and capability/version gates. Include deterministic Pester 6.2+ coverage, comment-based help, public documentation and unreleased notes in the same implementation PR. Use fail-closed fake adapters for side effects; no real installs, entitlement grants or settings changes in CI. Preserve original errors and distinguish unavailable, unknown, requested and completed outcomes.

Documented API references

• https://learn.microsoft.com/uwp/api/windows.applicationmodel.store.preview.installcontrol.appinstallmanager.cancel
• https://learn.microsoft.com/uwp/api/windows.applicationmodel.store.preview.installcontrol.appinstallitem.cancel

Start with parent #232 and dependencies #233, #234, and #236, then read the documented AppInstallManager.Cancel and AppInstallItem.Cancel APIs. Check the compiled-C# contract, access and version gates, and the required deterministic Pester coverage; done means all acceptance and shared delivery requirements are covered without real side effects.