fix: update validation tests for comparison rules and adjust schema definitions

[BaoDuong254]

Description

Implement missing comparison validator constraints and fix incorrect schema generation for eq_ignore_case, ne, ne_ignore_case, gt, gte, lt, and lte validate tags.

• Fix eq_ignore_case validator to generate a case-insensitive pattern instead of enum.
• Fix ne validator to generate not: { enum: [...] } for integer, number, string, boolean, and array types.
• Fix ne_ignore_case validator to generate not: { pattern: "^(?i)(...)$" } instead of incorrect schema.
• Implement gt/gte validators to generate minimum with exclusiveMinimum for integers/numbers, minLength for strings, and minItems for arrays.
• Implement lt/lte validators to generate maximum with exclusiveMaximum for integers/numbers, maxLength for strings, and maxItems for arrays.
• Add Not *SchemaObject field to SchemaObject to support the OpenAPI not keyword.
• Fix root cause of minimum/maximum never being serialized: Number and Integer embedded structs had conflicting JSON field names, causing encoding/json to silently drop both fields — resolved by moving minimum, maximum, exclusiveMinimum, and exclusiveMaximum directly onto SchemaObject.
• Fix stray u character syntax error in validate_comparision_test.go.
• Fix incorrect test expectation: lte=5 on string should produce maxLength: 5, not 6.
• Fix inconsistent test expectation: float64 format should be "float64" not "double" to match existing behavior.

Type of change

• 🐛 Bug fix
• ✨ New feature
• 🧹 Code cleanup / refactor
• 📚 Documentation update
• ⚙️ Other (please specify):