Support half-precision tolerance

[sethaxen]

This PR adds support for computing the action of the exponential at half-precision tolerance. It also ensures that the Taylor parameters are computed using double precision even if the eltype of the array has a much lower precision.

[codecov[bot]]

Codecov Report

Merging #6 (6ececce) into main (2579b81) will increase coverage by 0.05%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main       #6      +/-   ##
==========================================
+ Coverage   98.59%   98.64%   +0.05%     
==========================================
  Files           5        5              
  Lines          71       74       +3     
==========================================
+ Hits           70       73       +3     
  Misses          1        1              

Impacted Files	Coverage Δ
src/coefficients.jl	100.00% <100.00%> (ø)
src/parameters.jl	97.29% <100.00%> (+0.07%)	:arrow_up:
src/util.jl	100.00% <100.00%> (ø)

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