feat: add batch processing support for processing multiple files

Add comprehensive batch processing functionality to process multiple
accelerometer files from a folder in a single command.

Changes to src/accelerometer/accProcess.py:
- Add matchesExtension() to match file extensions with compression support
- Add discoverFiles() to discover files by extension with recursive option
- Add processSingleFile() extracted from main() for reusability
- Add processBatch() to orchestrate batch processing with error handling
- Add --fileExtensions argument (required for batch mode)
- Add --recursive argument for subdirectory search
- Refactor main() to detect and route file vs directory input
- Implement try-finally cleanup to ensure intermediate files deleted on error
- Catch SystemExit exceptions to prevent device.py sys.exit() from killing batch
- Detect duplicate basenames and exit with error to prevent data loss
- Exit with non-zero code when no files found or any files fail
- Respect --verbose flag for detailed error reporting in batch mode
- Remove unused atexit dependency (cleanup now in finally block)

Changes to README.md:
- Add batch processing usage section with examples
- Update output paths to reflect new outputs/{filename}/ structure
- Document --fileExtensions and --recursive options
- Explain compression format auto-detection

Key features:
- Serial processing with per-file error isolation
- Comprehensive batch summary with success/failure counts
- Exit codes: 255 for no files/duplicates, 1 for any failures
- Smart extension matching (case-insensitive, compression aware)
- Duplicate basename detection prevents output overwrites
- Backward compatible: single file mode unchanged

Author: chanshing

README.md

@@ -32,13 +32,15 @@ The following instructions make use of Anaconda to meet the minimum requirements
 You are all set! The next time that you want to use `accelerometer`, open the Anaconda Prompt and activate the environment (step 4). If you see `(accelerometer)` in front of your prompt, you are ready to go!
 
 ## Usage
+
+### Processing a single file
 To extract summary movement statistics from an Axivity file (.cwa):
 
 ```console
 $ accProcess data/sample.cwa.gz
 
- <output written to data/sample-outputSummary.json>
- <time series output written to data/sample-timeSeries.csv.gz>
+ <output written to outputs/sample/sample-summary.json>
+ <time series output written to outputs/sample/sample-timeSeries.csv.gz>
 ```
 
 Movement statistics will be stored in a JSON file:
@@ -58,6 +60,35 @@ See [Data Dictionary](https://biobankaccanalysis.readthedocs.io/en/latest/datadi
 
 Actigraph and GENEActiv files are also supported, as well as custom CSV files. See [Usage](https://biobankaccanalysis.readthedocs.io/en/latest/usage.html#basic-usage) for more details.
 
+### Batch processing multiple files
+To process multiple files in a folder, you must specify which file extensions to process:
+
+```console
+$ accProcess data/folder_with_cwa_files/ --fileExtensions cwa
+
+ <outputs written to outputs/file1/, outputs/file2/, etc.>
+```
+
+You can specify multiple extensions (comma-separated):
+
+```console
+$ accProcess data/my_data/ --fileExtensions cwa,bin,csv
+```
+
+The tool automatically includes compressed versions (.gz, .zip, .bz2, .xz), so `--fileExtensions cwa` will match both `.cwa` and `.cwa.gz` files.
+
+To search subdirectories recursively:
+
+```console
+$ accProcess data/my_data/ --fileExtensions cwa --recursive True
+```
+
+The batch processor will:
+- Automatically discover matching files
+- Process them serially with full error handling
+- Continue processing even if individual files fail
+- Provide a detailed summary of successful and failed files
+
 To plot the activity profile:
 ```console
 $ accPlot data/sample-timeSeries.csv.gz