Add Apple Watch companion app sideloading support

[Rzbck]

Summary

Adds sideloading support for iOS applications that embed an Apple Watch
companion under Watch/*.app.

Embedded Watch applications are now included in bundle identifier rewriting,
provisioning, signing, and installation instead of being treated as opaque
child bundles.

Changes

• discover embedded Apple Watch applications and nested app-ID-bearing bundles
• rewrite Watch bundle identifiers and WKCompanionAppBundleIdentifier
• provision iOS and watchOS App IDs separately
• register paired Apple Watch devices for development provisioning
• request watchOS-specific provisioning profiles
• sign embedded Watch application content
• install Watch companions through companion_proxy and streaming_zip_conduit
• use fresh companion-proxy connections for forwarded Watch services
• add unit coverage for watchOS provisioning and identifier rewriting

Validation

• builds successfully on Windows, macOS, and Linux
• cargo test -p isideload --lib passes
• the Watch installation path was validated during development on a physical iPhone with a paired Apple Watch
• the cleaned PR commit builds and passes its unit tests, but has not been separately re-run on physical hardware

Scope

This PR is limited to embedded Apple Watch companion applications.

HealthKit-specific capability handling is intentionally out of scope.
Independent Watch-only applications and every possible entitlement or nested
bundle configuration have not been validated.