feat: MultiContractKeystore (rebased)

[andy-haynes]

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[changeset-bot]

🦋 Changeset detected

Latest commit: ca580b1

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 10 packages

Name	Type
@near-js/keystores	Minor
@near-js/keystores-browser	Minor
@near-js/accounts	Patch
@near-js/keystores-node	Patch
near-api-js	Patch
@near-js/signers	Patch
@near-js/transactions	Patch
@near-js/wallet-account	Patch
@near-js/cookbook	Patch
@near-js/providers	Patch

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