524 bug 0143b7 (#525)

* Fix duplicate source file paths causing Vivado synthesis errors

- Fixed nested src/src/ directory structure that was causing duplicate module definitions
- When copying source files, don't append 'src' to output_dir since relative paths already include it
- This resolves Vivado synthesis errors about overwriting module definitions and unresolved hierarchical names
- Fixes issue where files were being added twice to Vivado project (once from src/ and once from src/src/)

Root cause: _copy_source_files was preserving directory structure from board_path,
which included 'src/', but was also being given an output_dir of 'board_output_dir/src',
resulting in files being placed at 'board_output_dir/src/src/file.sv'.

* Add regression tests for source file duplication bug

- test_copy_source_files_no_nested_src_directory: Verifies files aren't copied to src/src/
- test_unified_build_script_no_duplicate_source_files: Ensures build script doesn't add duplicate files

These tests prevent regression of GitHub issue #524 where duplicate module definitions
were causing Vivado synthesis to fail due to nested src/src/ directory structure.

* ..

v0.14.3-beta.6

fix (#520)

v0.14.4-beta.2

fancier script

v0.14.4-beta.1

fancier script