refactor: Extract func coerceValue from set and remove func set

[dylanahsmith]

cc @wisepythagoras

Problem

#145 is attempting to follow the current pattern of merging more code paths into set, which results in extra conditional complexity in set in order to essentially determine where it is called from and thus which argument to use.

Solution

The common functionality in the set function is value coercion, so just extract that to a separate function so that we can get rid of set.

Note that this makes all of these functions (coerceValue, Set, SetIdx) a lot more readable in isolation. In contrast, the call site for set makes it unclear why the placeholder arguments are passed in and the set function is harder to understand without knowing the context in which it is called from.

[codecov]

Codecov Report

Merging #149 (97dc1ff) into master (8d15ff3) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #149      +/-   ##
==========================================
+ Coverage   97.46%   97.48%   +0.01%     
==========================================
  Files          12       12              
  Lines         474      477       +3     
==========================================
+ Hits          462      465       +3     
  Misses          8        8              
  Partials        4        4              

Impacted Files	Coverage Δ
object.go	100.00% <100.00%> (ø)

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[wisepythagoras]

I like this solution. I'll incorporate it in #145 once it's merged.

[rogchap]

Reads better, thank you.