Merge asof float fix

[svenharris]

Fix bug with merge_asof when merging on floats and selecting a tolerance

• closes merge_asof doesn't allow float tolerance for float merges #22981
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[pep8speaks]

Hello @svenharris! Thanks for submitting the PR.

• There are no PEP8 issues in the file pandas/core/reshape/merge.py !

• There are no PEP8 issues in the file pandas/tests/reshape/merge/test_merge_asof.py !

[jreback]

lgtm ex comments

[codecov]

Codecov Report

Merging #22982 into master will decrease coverage by <.01%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master   #22982      +/-   ##
==========================================
- Coverage   92.18%   92.18%   -0.01%     
==========================================
  Files         169      169              
  Lines       50823    50828       +5     
==========================================
+ Hits        46853    46856       +3     
- Misses       3970     3972       +2

Flag	Coverage Δ
#multiple	90.6% <50%> (-0.01%)	⬇️
#single	42.36% <0%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/core/reshape/merge.py	93.89% <50%> (-0.26%)	⬇️

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[jreback]

lgtm. @mroeschke merge when satisfied

[mroeschke]

Thanks @svenharris