Add a precision assertion to BigMath test #387

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-latest 2.7	1m 2s
ubuntu-latest 3.0	37s
ubuntu-latest 3.1	32s
ubuntu-latest 3.2	35s
ubuntu-latest 3.3	34s
ubuntu-latest 3.4	35s
ubuntu-latest debug	38s
ubuntu-latest head	30s
macos-latest 2.7	1m 24s
macos-latest 3.0	28s
macos-latest 3.1	30s
macos-latest 3.2	23s
macos-latest 3.3	28s
macos-latest 3.4	28s
macos-latest debug	25s
macos-latest head	27s
macos-14 2.7	55s
macos-14 3.0	24s
macos-14 3.1	32s
macos-14 3.2	30s
macos-14 3.3	21s
macos-14 3.4	21s
macos-14 debug	34s
macos-14 head	36s
windows-latest 2.7	3m 57s
windows-latest 3.3	1m 48s
windows-latest 3.4	2m 56s
windows-latest head	1m 12s
windows-latest mingw	2m 44s
windows-latest mswin	1m 32s
	28m 2s

Provide feedback