feat: Make A/B tests independent (#7511)

## Explanation

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Right now, only the ID is used as a seed to determine what bucket the
user falls into in an A/B test.

Due to this, if there’s more than 1 A/B test configured, they will never
be independent of each other

**Solution:**
Optimizes threshold-based feature flag processing to ensure independent
user assignment across different flags. Define the distribution using
profile/metametrics ID + A/B test ID as a seed instead of just
profile/metametrics ID

**Key changes:**
- Use sha256 from @metamask/[email protected] to generate unique threshold
per flag (native crypto.subtle.digest - 10-100x faster)
- Persist threshold values in controller state to avoid recalculating on
app restart
- Skip cryptographic operations for non-threshold arrays
- Batch cache updates and cleanup into single state change
- Automatically remove stale cache entries when flags are deleted
- Remove @noble/hashes dependency (now available in @metamask/utils)

## References

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* Fixes #12345
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## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [x] 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)
- [ ] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them



<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Implements per-flag deterministic A/B assignment with cached
thresholds in the Remote Feature Flag Controller and upgrades
@metamask/utils to ^11.9.0 repo-wide.
> 
> - **Remote Feature Flag Controller**:
> - Implement per-flag threshold selection using `sha256(metaMetricsId +
flagName)` via `@metamask/utils@^11.9.0`.
> - Add `thresholdCache` to state; batch cache updates and clean up
stale entries; skip processing for non-threshold arrays.
> - Update tests and expectations; remove reliance on external hashing
utility.
> - **Dependencies**:
> - Upgrade `@metamask/utils` to `^11.9.0` across packages (yarn.lock
updated).
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
297369a. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Mark Stacey <[email protected]>

Author: MarioAslau

package.json

@@ -64,7 +64,7 @@
     "@metamask/eth-json-rpc-provider": "^6.0.0",
     "@metamask/json-rpc-engine": "^10.2.0",
     "@metamask/network-controller": "^27.1.0",
-    "@metamask/utils": "^11.8.1",
+    "@metamask/utils": "^11.9.0",
     "@ts-bridge/cli": "^0.6.4",
     "@types/jest": "^27.4.1",
     "@types/lodash": "^4.14.191",

packages/account-tree-controller/CHANGELOG.md

@@ -58,7 +58,7 @@
     "@metamask/snaps-sdk": "^9.0.0",
     "@metamask/snaps-utils": "^11.0.0",
     "@metamask/superstruct": "^3.1.0",
-    "@metamask/utils": "^11.8.1",
+    "@metamask/utils": "^11.9.0",
     "fast-deep-equal": "^3.1.3",
     "lodash": "^4.17.21"
   },

packages/account-tree-controller/package.json

@@ -61,7 +61,7 @@
     "@metamask/snaps-sdk": "^9.0.0",
     "@metamask/snaps-utils": "^11.0.0",
     "@metamask/superstruct": "^3.1.0",
-    "@metamask/utils": "^11.8.1",
+    "@metamask/utils": "^11.9.0",
     "deepmerge": "^4.2.2",
     "ethereum-cryptography": "^2.1.2",
     "immer": "^9.0.6",

packages/accounts-controller/CHANGELOG.md

@@ -51,7 +51,7 @@
     "@metamask/base-controller": "^9.0.0",
     "@metamask/controller-utils": "^11.17.0",
     "@metamask/messenger": "^0.3.0",
-    "@metamask/utils": "^11.8.1"
+    "@metamask/utils": "^11.9.0"
   },
   "devDependencies": {
     "@metamask/auto-changelog": "^3.4.4",

packages/accounts-controller/package.json

@@ -50,7 +50,7 @@
   "dependencies": {
     "@metamask/base-controller": "^9.0.0",
     "@metamask/messenger": "^0.3.0",
-    "@metamask/utils": "^11.8.1"
+    "@metamask/utils": "^11.9.0"
   },
   "devDependencies": {
     "@metamask/auto-changelog": "^3.4.4",