Made API to create field accept String

[jorgecarleitao]

When we already own the string, we should not need an extra allocation to create the field. This PR does this.

[codecov]

Codecov Report

Merging #643 (747ef82) into main (35dfab3) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #643   +/-   ##
=======================================
  Coverage   69.91%   69.91%           
=======================================
  Files         299      299           
  Lines       16628    16628           
=======================================
  Hits        11625    11625           
  Misses       5003     5003           

Impacted Files	Coverage Δ
src/datatypes/schema.rs	37.93% <ø> (ø)
src/datatypes/field.rs	44.68% <100.00%> (ø)

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