Feat/notify beyond first srp

[oilnam]

Explanation

• Expand notification account discovery from only the first HD keyring to all keyrings, so notification setup now includes addresses from HD, hardware, imported, and snap keyrings.
• Ensure notification account collection only keeps valid Ethereum hex addresses and deduplicates addresses across keyrings.
• Add backend push unlink support via DELETE /api/v2/token and invoke it when notification accounts are disabled (e.g. SRP/account removal), so backend can remove all linked Firebase tokens for those address/platform pairs.

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Medium Risk
Changes the set of accounts that will be registered for notifications and adds a new backend unlink call during account disablement, which could impact notification subscription state and cleanup behavior if misconfigured or if the endpoint behaves unexpectedly.

Overview
Notification setup now derives subscription accounts from all keyrings (not just the first HD/SRP), with address collection deduping, checksumming, and filtering to valid Ethereum hex addresses before creating on-chain triggers.

Adds a new NotificationServicesPushController:deletePushNotificationLinks messenger action and deleteLinksAPI (DELETE to the registration tokens endpoint) and wires it into NotificationServicesController.disableAccounts so removing/disablement of accounts also unlinks backend push-token associations for those address/platform pairs. Tests, mocks, exports, and changelog are updated accordingly.

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