test: split jsonpath_coverage_test.go into multiple files

Split into:
- jsonpath_coverage_basic_test.go (1040 lines, 27 tests)
- jsonpath_coverage_comprehensive_test.go (789 lines, 11 tests)
- jsonpath_coverage_edge_test.go (700 lines, 2 tests)
- jsonpath_coverage_final_test.go (548 lines, 1 test)

Coverage maintained at 89%

Author: oliveagle