refactor: improve CowEvcClosePositionWrapper test suite DRYness

Refactor CowEvcClosePositionWrapper test files to reduce code duplication
and improve maintainability:

Integration tests (CowEvcClosePositionWrapper.t.sol):
- Add helper functions for common test setup patterns
  - _createDefaultParams(): standardized param creation
  - _setupClosePositionApprovals(): approval setup for close position
  - _setupPreApprovedFlow(): pre-approved hash flow setup
  - _createPermitSignature(): permit signature creation
  - _encodeWrapperData(): wrapper data encoding
  - _executeWrappedSettlement(): settlement execution
- Add DEFAULT_SELL_AMOUNT and DEFAULT_BUY_AMOUNT constants
- Reduce test function size significantly while maintaining clarity

Unit tests (CowEvcClosePositionWrapper.unit.t.sol):
- Add helper functions for common patterns
  - _getDefaultParams(): returns default params (tests modify as needed)
  - _getEmptySettleData(): creates empty settlement data
  - _getSettleDataWithTokens(): creates settlement data with tokens/prices
  - _encodeWrapperData(): wrapper data encoding
  - _setupPreApprovedHash(): pre-approved hash setup
- Add DEFAULT_REPAY_AMOUNT and KIND_BUY constants
- Remove 5 redundant tests with no coverage impact:
  - test_Constructor_SetsName (trivial getter)
  - test_GetApprovalHash_Consistency (deterministic function)
  - test_ParseWrapperData_WithSignature (duplicate code path)
  - test_GetSignedCalldata_FullRepay (covered by other tests)
  - test_GetSignedCalldata_ContainsRepayItem (duplicate of RepayItem)
- Reduce from 32 to 27 unit tests with no loss in coverage

All tests pass: 7/7 integration tests, 27/27 unit tests

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: kaze-cow