fix: prevent intermittent proxy file missing errors in EcotoneLite tests

[dgafka]

Why is this change proposed?

EcotoneLite tests intermittently fail in CI with Failed opening required '/tmp/ecotone/.../ProxyFile.php' errors. This happens because ProxyFactory::dumpFile() silently ignores file_put_contents and rename failures, then proceeds to require a file that was never created.

Description of Changes

• Check return values in dumpFile(): file_put_contents and rename now throw ConfigurationException on failure instead of silently continuing. Temp files are cleaned up on rename failure.
• Defensive retry in loadProxyClass(): After initial proxy generation, if the file doesn't exist (stale stat cache or skipped generation), clears PHP stat cache and retries with forced overwrite before require.

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