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
Small analytics/history field change with a safe fallback; no transaction submission or auth logic is modified.

Overview
Bridge transaction history now records slippage from the quote instead of always storing 0, so post-submission Unified SwapBridge analytics (Submitted, Failed, Completed) can report the real slippage_limit / related MixPanel fields.

On SubmitStep.AddHistoryItem, slippagePercentage is set from quoteResponse.quote.slippage, with 0 when the field is missing. Tests and snapshots were updated to expect a non-zero slippage when the mock quote includes it.

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