Update documentation to reflect SQLite metrics output instead of CSV

[Copilot]

The README documentation was outdated and still referenced CSV files for metrics output, but MGPUSim has been updated to use SQLite databases instead. This caused confusion for users who expected to find metrics.csv files but instead found .sqlite3 files.

Changes Made

README.md:

• Updated the Getting Started section to mention .sqlite3 files and the mgpusim_metrics table instead of metrics.csv
• Added practical examples showing how to query the SQLite database to access metrics data
• Included sample SQL commands for viewing all metrics or filtering by component

Flag descriptions:

• Updated --report-all flag description to reference SQLite output
• Updated --metric-file-name flag description to reference SQLite files

Example Usage

After running a simulation with --report-all, users can now access metrics data using:

# View all metrics
sqlite3 your_simulation_file.sqlite3 "SELECT * FROM mgpusim_metrics;"

# View specific metrics for compute units
sqlite3 your_simulation_file.sqlite3 "SELECT * FROM mgpusim_metrics WHERE Location LIKE '%CU%';"

The SQLite format provides better structure and performance for large datasets compared to CSV, while maintaining all the same metrics information that was previously available.

Fixes #203.

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