Overhead caused by widening

[yuyichao]

After all, johnmyleswhite/Benchmarks.jl#36 is still present in this package....

julia> b1 = @benchmarkable rand($Float64); tune!(b1); run(b1)
BenchmarkTools.Trial:
  memory estimate:  16 bytes
  allocs estimate:  1
  --------------
  minimum time:     60.568 ns (0.00% GC)
  median time:      63.546 ns (0.00% GC)
  mean time:        71.347 ns (5.25% GC)
  maximum time:     25.763 μs (99.74% GC)
  --------------
  samples:          10000
  evals/sample:     982

julia> b2 = @benchmarkable rand(); tune!(b2); run(b2)
BenchmarkTools.Trial:
  memory estimate:  0 bytes
  allocs estimate:  0
  --------------
  minimum time:     3.432 ns (0.00% GC)
  median time:      3.962 ns (0.00% GC)
  mean time:        3.852 ns (0.00% GC)
  maximum time:     11.629 ns (0.00% GC)
  --------------
  samples:          10000
  evals/sample:     1000

AFAICT this affects BaseBenchmarks