Add synthetic financial ledger fixture with accounting negatives and currency conventions

[JohnnyWilson16]

Context

As part of our Contributor Roadmap (Level 1: Quick Wins), expanding realistic test fixtures ensures FreshData's financial data repairs remain robust across localized conventions without regressing.

Task

Add a synthetic financial ledger fixture in tests/fixtures/ demonstrating localized accounting conventions, such as parenthesized accounting negatives (e.g. (1,250.00)) and European currency formatting (e.g. EUR prefixes and mixed decimal separators).

Acceptance Criteria

• Create tests/fixtures/financial_ledger.csv with 20–50 rows of synthetic transaction records.
• Create accompanying tests/fixtures/financial_ledger.expectations.json specifying expected column dtypes and target values.
• Include common financial anomalies: accounting negatives (1,250.00), currency symbols (EUR, $), thousands commas, and whitespace.
• Add a unit test in tests/test_currency_locale.py or a dedicated test verifying fd.clean() handles the fixture accurately.
• All tests pass locally with pytest --no-cov.

Pointers

• Existing number & locale fixtures: tests/fixtures/locale_numbers.csv and tests/fixtures/locale_numbers.expectations.json
• Benchmark generator reference: benchmarks/fixtures/finance.py

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