Fix LinuxHardwareI2C fd lifecycle

[l5yth]

• Default i2c_file to -1; was 0 (stdin), so pre-begin() Wire ops blocked on stdin instead of failing fast.
• Only set hasBegun when open() succeeds, so a failed begin() can retry.
• Reset i2c_file to -1 in end() to avoid using a stale (or reused) fd.
• Fix Wire (LinuxHardwareI2C) defaults its fd to 0 (stdin), I2C ops before begin() block on stdin or run against the wrong fd #71

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