fix: gracefully handle BrokenPipeError when writing to closed pipes

[sentry]

This PR addresses an issue where the CLI would crash with a BrokenPipeError when its output (specifically error messages from click.echo()) was piped to another command that closed its input pipe prematurely (e.g., codecov do-upload --report-type test_results 2>&1 | head -n 0).

The root cause was that the CLI did not explicitly handle BrokenPipeError when writing to stdout or stderr in such scenarios, leading to an unhandled exception.

The solution implements two complementary approaches:

1. POSIX SIGPIPE handling: On POSIX systems, a SIGPIPE handler is installed (signal.signal(signal.SIGPIPE, signal.SIG_DFL)). This allows the operating system to terminate the process cleanly when a pipe's reading end is closed, preventing Python from raising a BrokenPipeError in many cases.
2. BrokenPipeError exception handling: The main cli() call in codecov_cli/main.py is wrapped in a try/except BrokenPipeError block. This catches any BrokenPipeError that might still occur (e.g., on Windows or in specific edge cases), silently flushes any remaining output, and exits with a non-zero status code (1) to indicate an issue, without crashing the application.

This ensures a more robust and user-friendly experience when interacting with the CLI in piped environments.

Fixes CLI-HC

_{@sentry <feedback>: Autofix iterates on these changes
@sentry stop iterating: Autofix stops iterating on this run}

_{This PR was automatically generated by Sentry. You can adjust this setting at any time.}

[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 1726 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.}