feat(keyring): enable P2TR taproot account creation

[marcopeereboom]

Explanation

The snap currently restricts account creation to P2WPKH only, enforced
by three guards in KeyringHandler documented as v1 restrictions. The
full P2TR pipeline already exists: @metamask/bitcoindevkit handles
taproot natively, caipToAddressType maps P2tr → 'p2tr',
Purpose.Taproot = 86 and purposeToAddressType are defined in
entities/account.ts, and the extension UI maps P2tr to 'Taproot'.
Only the whitelist checks block taproot.

This PR widens the whitelist to accept P2TR alongside P2WPKH:

• createAccount: accept BtcAccountType.P2tr in address type validation
• #extractAddressType: accept BIP-86 (purpose 86) derivation paths
• discoverAccounts: include P2TR in the address type discovery list

No new dependencies. No changes to BDK integration, CAIP mappings, or
account infrastructure. Existing P2WPKH behavior is unchanged.

References

• Companion PR: feat(connect): support ordinals purpose for P2TR addresses bitcoin-wallet-standard#30
• BIP-86: Key Derivation for Single Key P2TR Outputs
• BIP-341: Taproot (SegWit version 1 spending rules)

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
Expands supported account types and derivation-path validation, and doubles discovery calls (P2WPKH + P2TR) which can impact account creation/discovery behavior across networks. While scoped to whitelisting/validation, it touches keyring account flows that affect wallet state and UX.

Overview
Enables Taproot (P2TR) accounts alongside existing P2WPKH in KeyringHandler.

createAccount now accepts BtcAccountType.P2tr, validates defaults accordingly, and #extractAddressType permits BIP-86 (purpose 86) derivation paths (updating related error messages). discoverAccounts is expanded to include P2TR in discovery, and tests/changelog are updated to cover the new behavior.

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[Nabilislam722]

I would Love to see this. This is Massive TBH P2TR taproot account creation system on MetaMask is personally needed...

[Nabilislam722]

Utilizing it.each for the derivation path tests is a great way to handle the matrix of Bitcoin address types BIP-84 for p2wpkh

[marcopeereboom]

FWIW, I tested all of this code using metamask flask and I was able to send and move ordinals.

[Battambang]

There is already this Taproot PR #578 opened. Pending due to updates in MM clients to QA.

[marcopeereboom]

@Battambang Aware of #578, but this PR is complete and tested end-to-end: I ran it with MetaMask Flask, created P2TR accounts, and sent and moved ordinals with it. From my side this code works and is ready to deploy. If #578 is still pending on client QA, this one is ready to go now — happy to coordinate on any overlap.