[INLONG-11237][SDK] Transform SQL supports CHAR_LENGTH function

[Zkplo]

Fixes #11237

Motivation

1. Fixed the handling of different character sets in LengthFunction and added relevant test cases.
2. Add the CharLengthFunction class and enhance the corresponding test class: TestCharLengthFunction

Modifications

Verifying this change

(Please pick either of the following options)

• This change is a trivial rework/code cleanup without any test coverage.

• This change is already covered by existing tests, such as:
  (please describe tests)

• This change added tests and can be verified as follows:

  (example:)

  • Added integration tests for end-to-end deployment with large payloads (10MB)
  • Extended integration test for recovery after broker failure