abseil-duration-unnecessary-conversion

Finds and fixes cases where absl::Duration values are being converted to numeric types and back again.

Examples:

// Original - Conversion to double and back again
absl::Duration d1;
absl::Duration d2 = absl::Seconds(absl::ToDoubleSeconds(d1));

// Suggestion - Remove unnecessary conversions
absl::Duration d2 = d1;


// Original - Conversion to integer and back again
absl::Duration d1;
absl::Duration d2 = absl::Hours(absl::ToInt64Hours(d1));

// Suggestion - Remove unnecessary conversions
absl::Duration d2 = d1;

Note: Converting to an integer and back to an absl::Duration might be a truncating operation if the value is not aligned to the scale of conversion. In the rare case where this is the intended result, callers should use absl::Trunc to truncate explicitly.