feat(keyring-controller): add filter selector callback to withKeyring

[ccharly]

Explanation

Adding a new way to filter out keyring instances with withKeyring.

The idea is to be able to filter by keyring instance logic/property. Since KeyringObject data are pretty limited, we cannot do things like:

const specificKeyring = controller.withKeyring({
  filter: (keyring): keyring is MyKeyring => {
    return isMyKeyring(keyring) && keyring.useSpecificMethodOrProp() !== undefined;
  },
}, ({ keyring }) => {
  // `keyring` is inferred as `MyKeyring` here, so `filter` type-predicate is also
  // used in type inference in the `operation` callback!
  ...
});

Here, the useSpecificMethodOrProp is specific to MyKeyring type.

References

N/A

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

---

Note

Medium Risk
Touches keyring selection logic in withKeyring, so incorrect predicate handling or selection order could affect any caller using the new variant, though coverage is strong and the change is localized.

Overview
Extends KeyringController.withKeyring to support selecting a keyring via a new KeyringSelector variant { filter: ({ keyring, metadata }) => boolean }, which picks the first keyring matching the predicate.

Adds a focused test suite covering filter-based selection (result passthrough, metadata availability, first-match behavior, and error cases like KeyringNotFound/UnsafeDirectKeyringAccess) and documents the addition in the package changelog.

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