Feature/closed pnl fill (backport #3168)

[mergify]

Changelist

• New Features
  • Added position state snapshot fields to fill records to capture position metrics at execution time.
  • Added realized P&L tracking field to perpetual positions.
  • Updated realized P&L calculation to use stored position data instead of derived computation.

Test Plan

Added new tests to check for the inclusion of the before field entries and updated existing ones to support the new fill schema.

Author/Reviewer Checklist

• If this PR has changes that result in a different app state given the same prior state and transaction list, manually add the state-breaking label.
• If the PR has breaking postgres changes to the indexer add the indexer-postgres-breaking label.
• If this PR isn't state-breaking but has changes that modify behavior in PrepareProposal or ProcessProposal, manually add the label proposal-breaking.
• If this PR is one of many that implement a specific feature, manually label them all feature:[feature-name].
• If you wish to for mergify-bot to automatically create a PR to backport your change to a release branch, manually add the label backport/[branch-name].
• Manually add any of the following labels: refactor, chore, bug.

Summary by CodeRabbit

• New Features

  • Fill responses now include pre-trade position state: position size, entry price, and position side before each fill.
  • Perpetual position data now exposes a totalRealizedPnl field; reported realized PnL in responses is sourced from this stored value.

• Documentation

  • Public API schemas and examples updated to show the new fill fields and the totalRealizedPnl presence.

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This is an automatic backport of pull request #3168 done by [Mergify](https://mergify.com).

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