fix: Prevent AttributeError in Sentry cleanup and optimize gcov plugin

[sentry]

This PR addresses issue CLI-GN, which manifested as an AttributeError: 'NoneType' object has no attribute 'get' during the 'Do Upload' transaction.

The root cause was a combination of two factors:

1. Unbounded Gcov plugin scan: The gcov plugin, when enabled, would perform an exhaustive search for .gcno files across the entire project directory, including large vendor directories like node_modules. This often led to extremely long runtimes and subsequent KeyboardInterrupt signals (e.g., due to CI timeouts).
2. Fragile Sentry exception handling: During the cleanup phase of a Sentry transaction, specifically within the _before_send hook, the code was attempting to call .get() on potentially None values within the exception event structure. This would occur when a KeyboardInterrupt (or similar exception) was being processed, leading to the AttributeError.

Changes implemented:

• Gcov plugin: Modified codecov_cli/plugins/gcov.py to include node_modules, .git, and vendor in the default folders_to_ignore list for the GcovPlugin. This prevents the plugin from scanning these large, irrelevant directories by default, significantly reducing scan times and the likelihood of timeouts.
• Sentry _before_send: Updated codecov_cli/opentelemetry.py to make the .get() calls within the _before_send function more robust. It now explicitly handles cases where intermediate dictionary keys might have None values, preventing the AttributeError during exception processing.

Fixes CLI-GN

_{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

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