Release/961.0.0

[gambinish]

Explanation

This PR releases major version bump of perps-controller to v6.0.0

References

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
Low code-change risk (version/changelog only), but medium integration risk because @metamask/perps-controller is released as a new major version with documented breaking API field renames that consumers must adopt.

Overview
Publishes a new release by bumping the monorepo version to 961.0.0 and @metamask/perps-controller to 6.0.0.

Updates packages/perps-controller/CHANGELOG.md with a new 6.0.0 section (including noted breaking AccountState balance field renames) and adjusts the compare links for the new release tag.

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[gambinish]

Claiming this release number as 960.0.0 has been already claimed. If once 960 gets merged and rebased, we can remove the DO-NOT-MERGE label and merge