[perps-controller] Make Hyperliquid max withdrawable decimal-safe - #11253

Explanation

Hyperliquid unified-account balances were aggregated with native JavaScript numbers. Equivalent six-decimal spot.total - spot.hold inputs could therefore emit different strings and differ by one atomic USDC unit after conversion.

This change:

• performs spot collateral subtraction and multi-DEX balance aggregation with BigNumber;
• retains the exact perps subtotal until spot collateral has been included, then canonicalizes once to the supported six-decimal precision;
• reuses the decimal-safe account aggregator for streamed account updates;
• preserves genuine one-micro-USDC changes and existing sentinel behavior.

Focused regressions cover both reported operand pairs, fractional perps plus fractional spot collateral, final-only rounding across DEXs, a genuine one-micro-USDC change, streamed values, and the public Hyperliquid account-state path with isolated positions on main and HIP-3 DEXs.

Contract impact

Consumer compatibility

MetaMask Mobile at eb837f5316d was checked at the transaction-pay balance consumers. They already convert withdrawableBalance with BigNumber, so canonical six-decimal strings require no migration. No Extension checkout was available in this workspace; the published type and API shape are unchanged.

References

• TAT-4345

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