Harmonise WIN32 and POSIX serial comms timeout

[mcuee]

This is from @mariusgreuel in Issue #1249.

• Harmonize WIN32 implementation of serial time-outs with Posix one #1249

The WIN32 time-out is specified as ReadTotalTimeoutConstant + buflen * ReadTotalTimeoutMultiplier, which makes it potentially much longer than the POSIX one (i.e. at least double). ReadIntervalTimeout is also set to timeout, which essentially renders the interval timeout ineffective, so IMHO, we should explicitly disable that feature.

[mcuee]

I've carried some tests and it seems to work. However, as mentioned by @mariusgreuel, this needs more tests.

#1249 (comment)

However, this probably needs some extensive testing for those programmers where the time-out is carefully chosen to match the requirements.

See https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/ntddser/ns-ntddser-_serial_timeouts

[mcuee]

COMMTIMEOUTS structure (winbase.h)
https://learn.microsoft.com/en-us/windows/win32/api/winbase/ns-winbase-commtimeouts

typedef struct _COMMTIMEOUTS {
  DWORD ReadIntervalTimeout;
  DWORD ReadTotalTimeoutMultiplier;
  DWORD ReadTotalTimeoutConstant;
  DWORD WriteTotalTimeoutMultiplier;
  DWORD WriteTotalTimeoutConstant;
} COMMTIMEOUTS, *LPCOMMTIMEOUTS;

[stefanrueger]

I agree with this PR. After reading up on the COMMITTIMEOUTS structure had come to the same conclusion as @mariusgreuel. Quite a few users and applications will be affected by the change. Let's cross our fingers that this is not one of those situations where a particular application relied on the larger timeout (without AVRDUDE knowing about it). But yes, it's better to make this change now than 10 seconds before the release of 7.3 as, if it breaks something, we might hear back before 7.3

[mcuee]

@stefanrueger

Glad to hear that you agree with this PR. I agree with you that it is better to merge this soon so that issues will be reported within the next two months.