refactor!: remove cacheEncryptionKey flag from KeyringController (#7127)

## Explanation

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This PR includes part of the changes originally proposed in [this
PR](#5963) that were inflating its
size:
- Remove the `cacheEncryptionKey` flag from `KeyringController`
constructor options and instance variables
- All code paths that used this flag have been removed (effectively, the
controller behaves as if the flag was always `true`)
- `GenericEncryptor` and `ExportableKeyEncryptor` have been merged into
a single `Encryptor` type.
- The `Encryptor` type has also been fixed to be compatible with
`@metamask/browser-passworder` and `Encryptor` from mobile
- As `Encryptor` now accepts type parameters to specify encryption key
and derivation params types, the `KeyringController` has been updated to
accept these type parameters and pass them to the `Encryptor` instance.

## References

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* Related to #6010

## 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](https://github.com/MetaMask/core/tree/main/docs/contributing.md#updating-changelogs),
highlighting breaking changes as necessary
- [ ] I've prepared draft pull requests for clients and consumer
packages to resolve any breaking changes

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Unifies the encryptor interface with a new generic `Encryptor`,
removes `cacheEncryptionKey` and requires an `encryptor` for
`KeyringController`, adds a derivation-options type param to
`SeedlessOnboardingController`, and updates tests/types accordingly.
> 
> - **Keyring Controller**:
> - Replace `GenericEncryptor`/`ExportableKeyEncryptor` with a single
generic `Encryptor` (supports key import/export, detailed
encrypt/decrypt, custom result types).
> - Add generic type params `EncryptionKey`,
`SupportedKeyDerivationOptions`, and `EncryptionResult` to
`KeyringController` and `KeyringControllerOptions`.
> - BREAKING: `encryptor` is now required; remove `cacheEncryptionKey`
and related paths/state handling.
>   - Fix `decryptWithKey` typing to accept encryption result object.
> - **Seedless Onboarding Controller**:
> - Add optional `SupportedKeyDerivationOptions` type parameter; update
`VaultEncryptor` to use unified `Encryptor`.
> - **Tests/Mocks**:
> - Refactor tests to new encryptor API; remove branches for
`cacheEncryptionKey`; add `createVault` helper and adjust mocks to new
types.
> - **Changelogs/Config**:
> - Update package changelogs to document breaking changes and new
generics.
>   - Slightly lower Jest coverage thresholds for `keyring-controller`.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
16f68c7. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Frederik Bolding <frederik.bolding@gmail.com>

Author: mikesposito

packages/keyring-controller/CHANGELOG.md

@@ -7,6 +7,26 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Added optional `EncryptionKey`, `SupportedKeyDerivationOptions` and `EncryptionResult` type parameters to the `KeyringController`, `ExportableKeyEncryptor` and `KeyringControllerOptions` types ([#7127](https://github.com/MetaMask/core/pull/7127))
+  - This type parameter allows specifying the encryption key, key derivation options and encryption result types supported by the injected encryptor, defaulting to `@metamask/browser-passworder` types.
+
+### Changed
+
+- **BREAKING:** The `KeyringController` constructor options now require an encryptor ([#7127](https://github.com/MetaMask/core/pull/7127))
+  - The `encryptor` constructor option was previously optional and defaulted to an instance of `@metamask/browser-passworder`.
+- **BREAKING:** The `GenericEncryptor` and `ExportableKeyEncryptor` types have been merged into a single `Encryptor` type ([#7127](https://github.com/MetaMask/core/pull/7127))
+
+### Removed
+
+- **BREAKING:** The `cacheEncryptionKey` parameter has been removed from the `KeyringController` constructor options ([#7127](https://github.com/MetaMask/core/pull/7127))
+  - This parameter was previously used to enable encryption key in-memory caching, but it is no longer needed as the controller now always uses the latest encryption key.
+
+### Fixed
+
+- Fixed incorrect type for `decryptWithKey` method of `ExportableKeyEncryptor` (now `Encryptor`) ([#7127](https://github.com/MetaMask/core/pull/7127))
+
 ## [24.0.0]
 
 ### Changed

packages/keyring-controller/jest.config.js

@@ -17,10 +17,10 @@ module.exports = merge(baseConfig, {
   // An object that configures minimum threshold enforcement for coverage results
   coverageThreshold: {
     global: {
-      branches: 95.78,
+      branches: 94.03,
       functions: 100,
-      lines: 98.68,
-      statements: 98.69,
+      lines: 98.31,
+      statements: 98.33,
     },
   },