Add errno checking and debug logging for remove() failures in TOCTOU fix

[Copilot]

Addresses feedback on PR #143: the TOCTOU fix correctly eliminated the race condition between stat() and remove(), but silently ignored all remove() failures, potentially hiding legitimate errors like permission denials.

Changes

• Added errno checking: Modified remove() call to check return value and examine errno
• Added debug logging:
  • ENOENT → logged as "expected race condition" (file already removed by another thread)
  • Other errors (e.g., EACCES) → logged with errno and strerror() for troubleshooting
• Added includes: <cerrno> and <cstring> for errno/strerror support

Implementation

// Before
(void)remove(DIRECT_BLOCK_FILENAME);

// After
if (remove(DIRECT_BLOCK_FILENAME) != 0) {
    int err = errno;
    if (err == ENOENT) {
        RDK_LOG(RDK_LOG_DEBUG, LOG_RFCMGR,"[%s][%d] RFC: %s already removed (expected race condition)\n", ...);
    } else {
        RDK_LOG(RDK_LOG_DEBUG, LOG_RFCMGR,"[%s][%d] RFC: Failed to remove %s, errno=%d (%s)\n", ..., err, strerror(err));
    }
}

Uses DEBUG level to avoid noise in production while maintaining visibility for diagnostics.

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