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/derivation paths in keyring account creation and discovery, which can affect address derivation and account selection flows. Changes are scoped to whitelisting/validation and test coverage is updated, but incorrect mappings could lead to wrong accounts being created or discovered.

Overview
Adds taproot support by allowing BtcAccountType.P2tr alongside P2wpkh when creating accounts in KeyringHandler, including validating defaults and addressType/derivation-path consistency.

Updates derivation-path parsing to accept BIP-86 (purpose 86) in addition to BIP-84, and expands discoverAccounts to scan both P2WPKH and P2TR across all scopes (with corresponding unit test updates).

Documents the new P2TR creation/discovery behavior in the snap package changelog.

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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.