fix: FirebaseProvider claimed visionOS support Firebase does not have (2.1.1)

[AndrewKochulab]

Found by dry-running the CocoaPods validation before publishing, rather than discovering it after an irreversible trunk push.

The bug

The package advertised visionOS for the Firebase adapter. Firebase gates FirebaseAnalytics to iOS/macCatalyst/macOS/tvOS — no visionOS. So:

swift build --traits Firebase --triple arm64-apple-xros1.0-simulator
# error: no such module 'FirebaseAnalytics'

Present in both 2.0.0 and 2.1.0.

Same mistake in the podspec: the Firebase, Mixpanel and Bugsnag subspecs inherited visionOS from the root spec while the vendors' own podspecs omit it, so pod lib lint failed on four errors. Each subspec now declares the platform set its dependency actually supports.

Worth noting the two manifests legitimately differ here: Mixpanel and Bugsnag do build for visionOS under SwiftPM — only their CocoaPods specs leave it out.

Why CI missed it

The gap was shaped exactly like the bug:

Job	Platforms	Traits
platforms	all 5	none
providers	macOS host only	all 4

No provider adapter was ever compiled for a non-host platform — precisely where a vendor's own platform gating bites. The full matrix, run locally, isolates it:

          iOS       tvOS      watchOS   visionOS  macOS
Firebase  ok        ok        ok        FAIL      ok
Facebook  ok        ok        ok        ok        ok
Mixpanel  ok        ok        ok        ok        ok
Bugsnag   ok        ok        ok        ok        ok

This PR adds a provider-platforms job covering all 20 combinations. Verified locally that it fails on the unfixed code and passes on the fix.

Consequence for CocoaPods

2.0.0 and 2.1.0 cannot be published to the trunk — their podspecs fail validation for this reason, and correcting them would mean rewriting already-published tags. 2.1.1 will be the first 2.x on CocoaPods; pod users go from 1.0.0 straight to it, skipping both affected versions.

SwiftPM users on 2.1.0 are unaffected unless they build the Firebase trait for visionOS.

Verification

• Full provider × platform matrix green (20/20)
• pod lib lint --allow-warnings, all subspecs, all platforms: passed (previously 4 errors)
• 96 tests, 0 lint violations, zero-dependency invariant intact, iOS integration build OK

No API or behaviour changes.

🤖 Generated with Claude Code