Add a randomized test for 'frozen' DEX offers.

[dmkozh]

Description

Removal of offers that would affect frozen entries from DEX has already been covered in a simple smoke test. This is a more robust randomized test that ensures that DEX behavior is the same both with and without 'frozen' offers.

Checklist

• Reviewed the contributing document
• Rebased on top of master (no merge commits)
• Ran clang-format v8.0.0 (via make format or the Visual Studio extension)
• Compiles
• Ran all tests
• If change impacts performance, include supporting evidence per the performance document

[Copilot]

Pull request overview

Adds a new randomized acceptance test to validate that offers owned by accounts with frozen ledger keys do not perturb DEX matching outcomes (i.e., matching results and account balance deltas remain identical to a baseline run without frozen offers).

Changes:

• Introduces a randomized market simulation that runs twice per iteration (baseline vs. with frozen offers) and compares resulting balance deltas for taker + active makers.
• Adds aggregate assertions intended to ensure the test actually exercised both successful transactions and frozen-offer removals.