Fix ResourceWarning: unclosed database in SqliteReader and unit tests

[yunzheng]

• SqliteReader was missing a close() method
• sqlite3.Connection as a context manager does NOT close the connection it only commits or rolls back the transaction.

resolves #209

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.35%. Comparing base (c3f8cd8) to head (1650e5c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #210      +/-   ##
==========================================
+ Coverage   83.33%   83.35%   +0.01%     
==========================================
  Files          35       35              
  Lines        3714     3718       +4     
==========================================
+ Hits         3095     3099       +4     
  Misses        619      619              

Flag	Coverage Δ
unittests	83.35% <100.00%> (+0.01%)	⬆️

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[Copilot]

Pull request overview

This pull request fixes ResourceWarning about unclosed database connections in Python 3.13+ by implementing proper resource cleanup for SQLite connections.

Changes:

• Added a close() method to SqliteReader to properly close database connections
• Updated test cases to use closing() context manager for explicit connection cleanup
• Added explicit commit() calls in tests where data persistence is required

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
flow/record/adapter/sqlite.py	Implements close() method in SqliteReader to properly close database connections
tests/adapter/test_sqlite_duckdb.py	Updates all test cases to use closing() wrapper and adds explicit commit() calls for proper transaction handling

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