Fix #1332, Resolve compiler warnings re. signedness comparisons

[thnkslprpt]

Checklist

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to [email protected] and copied [email protected].

Describe the contribution

• Partially fixes Resolve signed/unsigned comparison warnings #1332 - only flight code was amended. Warnings for test code still exist.
  • MinSystemState represents CFE_ES_SystemState values. Seems safe (and future-proof) to cast to a simple int given the possible range of these values.
  • ElapsedTime casted to int64_t instead of int/int32 to guarantee no conceivable chance of overflow even with (very) large msec time values.
  • BlockSize used to represent the size of various structures - fine to cast to standard int.
  • StringLength type changed to size_t (more correct given it's usage, and avoids 2 signedness comparison warnings).
  • RecordSize represents number of bytes - maybe safest with int64_t.
  • TblSizeInBytes represents number of bytes (safest with int64_t)

Testing performed
GitHub CI actions (incl. Build + Run, Unit Tests etc.) all passing successfully.
Tested locally with -Wsign-compare flag enabled - no warnings issued for cFE.

Expected behavior changes
No change to behavior.

Contributor Info
Avi Weiss @thnkslprpt