[Fix #468] Fix false positives for Performance/BigDecimalWithNumericArgument

[koic]

Fixes #468.

This PR fixes false positives for Performance/BigDecimalWithNumericArgument when using float argument for BigDecimal.

In Ruby 3.1 and later, cases where numbers are faster than strings are limited to Integer. For Float, strings are still faster:

$ cat example.rb
require 'benchmark/ips'
require 'bigdecimal'
require 'bigdecimal/util'

Benchmark.ips do |x|
  x.report('float string')             { BigDecimal('4.2') }
  x.report('float with prec')          { BigDecimal(4.2, Float::DIG + 1) }
  x.report('to_d string without prec') { '4.2'.to_d }
  x.report('to_d float without prec')  { 4.2.to_d }
  x.report('to_d float with prec')     { 4.2.to_d(Float::DIG + 1) }
  x.compare!
end

ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [x86_64-darwin22]
Warming up --------------------------------------
        float string   246.214k i/100ms
     float with prec   173.880k i/100ms
to_d string without prec
                       255.950k i/100ms
to_d float without prec
                       181.033k i/100ms
to_d float with prec   151.091k i/100ms
Calculating -------------------------------------
        float string      2.418M (± 5.5%) i/s -     12.064M in   5.004969s
      float with prec      1.685M (± 4.0%) i/s -      8.520M in   5.064059s
to_d string without prec
                          2.460M (± 4.2%) i/s -     12.286M in   5.002392s
to_d float without prec
                          1.781M (± 6.5%) i/s -      8.871M in   5.007829s
to_d float with prec      1.584M (± 5.7%) i/s -      8.008M in   5.072184s

Comparison:
to_d string without prec:  2460462.7 i/s
        float string:  2418003.6 i/s - same-ish: difference falls within error
to_d float without prec:  1781070.6 i/s - 1.38x  slower
     float with prec:  1685372.9 i/s - 1.46x  slower
to_d float with prec:  1584419.5 i/s - 1.55x  slower

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