Fix default UNITY_INCLUDE_EXEC_TIME macros

[Angel2Eyes]

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Problem

UNITY_INCLUDE_EXEC_TIME cannot be used with -Werror=sign-conversion. On Windows the default UNITY_PRINT_EXEC_TIME assigns a signed clock_t delta to UNITY_UINT. Two of the three print macros are also brace blocks rather than statements, so MACRO(); is not if/else safe. CI never compiled this optional path, so it could rot.

Unix already uses clock_gettime(CLOCK_MONOTONIC) (with casts and do/while) when that clock exists. That path is unchanged.

Fix

• Cast signed time deltas to UNITY_UINT and use do { } while (0) on the Windows and UNITY_CLOCK_MS print macros.
• If Unix/macOS has no CLOCK_MONOTONIC in <time.h>, fall back to ISO C clock().
• Add make execTimeDetection and run it from rake ci.

Closes #838.

Verification

• unity.c compiles with MSVC with and without -DUNITY_INCLUDE_EXEC_TIME.
• This environment has no gcc/make, so make test / rake ci were not run locally. GitHub Actions rake ci now includes execTimeDetection.