fix: handle FileNotFoundError for temporary coverage files

[sentry]

This PR addresses CLI-48, a FileNotFoundError occurring when the upload-coverage command attempts to read temporary coverage files (e.g., .tmp/coverage-N.json) that have been deleted between discovery and the actual read operation. This is a TOCTOU (time-of-check-time-of-use) race condition.

The fix involves wrapping the file reading operations in codecov_cli/services/upload/upload_sender.py (_get_files) and codecov_cli/services/upload/legacy_upload_sender.py (_generate_coverage_files_section) with try-except FileNotFoundError blocks. If a file is no longer found, it is now gracefully skipped, and a warning is logged, preventing the entire upload command from crashing.

Fixes CLI-48

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
723	1	722	1

View the full list of 1 ❄️ flaky test(s)

api.temp.calculator.test_calculator::test_divide

Flake rate in main: 100.00% (Passed 0 times, Failed 1625 times)

Stack Traces | 0.001s run time

def
                test_divide():
                > assert Calculator.divide(1, 2) == 0.5
                E assert 1.0 == 0.5
                E + where 1.0 = <function Calculator.divide at 0x104c9eb90>(1, 2)
                E + where <function Calculator.divide at 0x104c9eb90> = Calculator.divide
                .../temp/calculator/test_calculator.py:30: AssertionError

To view more test analytics, go to the Test Analytics Dashboard
_{📋 Got 3 mins? Take this short survey to help us improve Test Analytics.}