fix(runtime): remove unused OAuthTokenRequestBody interface

[JonasJesus42]

• Remove unused interface that was causing TS6196 errors in MCPs
• Bump version to 1.2.8 to trigger npm publish

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Summary by cubic

Removed an unused OAuthTokenRequestBody interface in the runtime to fix TS6196 errors in MCPs. Bumped the package version to 1.2.8 to publish the fix.

^{Written for commit 00b1335. Summary will update on new commits.}

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[cubic-dev-ai]

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