ranges: Add index64_t constructor and deprecate index_t version

[stotko]

The memory and iterator modules consistently use index64_t to specify sizes. However, ranges uses the configurable index_t type which may be different from index64_t. Add a corresponding index64_t constructor version to both device_range and host_range and deprecate the index_t version (only implicitly to avoid unnecessary noise).

[codecov]

Codecov Report

Merging #102 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #102      +/-   ##
==========================================
+ Coverage   97.82%   97.83%   +<.01%     
==========================================
  Files          27       27              
  Lines        1609     1613       +4     
==========================================
+ Hits         1574     1578       +4     
  Misses         35       35

Impacted Files	Coverage Δ
src/stdgpu/impl/ranges_detail.h	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f98ee52...09b1e37. Read the comment docs.