fix: include quote slippage value in MixPanel event properties

[micaelae]

Explanation

Saves the QuoteResponse["quote"]["slippage"] value in the txHistory to populate the Submitted, Failed and Completed MixPanel events

References

Fixes https://consensyssoftware.atlassian.net/browse/SWAPS-4446

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

Low Risk
Analytics-only fix on history field population; no change to submission or swap execution logic.

Overview
Bridge transaction history now records slippage from the submitted quote instead of always storing 0.

On SubmitStep.AddHistoryItem, slippagePercentage is set from quoteResponse.quote.slippage (with 0 when missing). That value is persisted on the history item so Unified SwapBridge Submitted, Failed, and Completed MixPanel events can report the correct slippage-related properties.

Tests and snapshots were updated to expect slippage: 0.01 on the quote and slippagePercentage: 0.01 on the history item.

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