Use internal visibility for fn level hash method defs

[cgewecke]

#651, #649

Excludes contract level instrumentation from the contract's public interface.

This doubles the line hits for some reason...nbd - we already have this problem on the beta with the boolean hash methods.

[codecov-commenter]

Codecov Report

Merging #660 (d09b0b7) into master (4c2410d) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #660   +/-   ##
=======================================
  Coverage   98.68%   98.68%           
=======================================
  Files          22       22           
  Lines         991      991           
=======================================
  Hits          978      978           
  Misses         13       13           

Impacted Files	Coverage Δ
lib/injector.js	100.00% <100.00%> (ø)

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