refactor(codegen): Split large files in pkg/translate/ for improved maintainability

Split three oversized files into 17 focused modules to improve code
organization and maintainability. This is a pure refactoring with zero
behavioral changes, verified by test-harness showing identical generated code.

Changes:
- Split terraform_provider/funcs.go (3,428 lines) → 9 files:
  * encryption.go - Encrypted value handling
  * conversion.go - Terraform/Pango data conversion
  * location.go - Location struct and schema generation
  * schema.go - Terraform schema generation
  * import_state.go - Import state handling
  * structs_model.go - Terraform model struct generation
  * crud_operations.go - CRUD operations (Create/Read/Update/Delete)
  * ephemeral_operations.go - Ephemeral resource operations
  * utils.go - Shared utilities

- Split structs.go (1,029 lines) → 5 files:
  * template_utils.go - Template loading utilities
  * import_location.go - Import and location rendering
  * type_calculation.go - Type and tag calculation
  * struct_generation.go - Struct creation and rendering
  * xml_marshaling.go - XML marshaling and containers

- Split terraform_provider/terraform_provider_file.go (713 lines) → 3 files:
  * generator.go - Core generator orchestration
  * entity_generators.go - Entity-specific generation
  * provider_generators.go - Provider-level generation

Metrics:
- Largest file reduced from 3,428 to 471 lines (86% reduction)
- All files now under 750 lines
- Average file size: ~250 lines
- Zero files over 500 lines (previously 3)

Verification:
- All tests pass (make test/codegen)
- Generated code identical to baseline (codegen-diff)
- No circular dependencies
- No compilation errors

This refactoring improves code navigability, makes reviews easier, and
reduces cognitive load by organizing code into single-responsibility modules.

Author: kklimonda-cl