[Improve][connector-assert]support 'DECIMAL' type and fix 'Number' type precision issue

[NickCodeJourney]

when I use float type data test
https://user-images.githubusercontent.com/72905543/267356692-616eed7f-3ede-4ca9-bdaa-f18f4a496ee6.png

Purpose of this pull request

Check list

• Code changed are covered with tests, or it does not need tests for reason:
• If any new Jar binary package adding in your PR, please add License Notice according
  New License Guide
• If necessary, please update the documentation to describe the new feature. https://github.com/apache/seatunnel/tree/dev/docs
• If you are contributing the connector code, please check that the following files are updated:
  1. Update change log that in connector document. For more details you can refer to connector-v2
  2. Update plugin-mapping.properties and add new connector information in it
  3. Update the pom file of seatunnel-dist
• Update the release-note.

waiting for ci check

[ruanwenjun]

LGTM