Add IN6 rule: Continuation Line

[me-cr]

This PR introduces the style rule IN6: Continuation Line, to the lint module: updates the configuration and rule system to support it, and adds thorough tests to validate the behavior.

Code Changes

• Configuration:
  Added indent_continuation_line to LintCfg with default options.
  Updated default configuration and setup logic to support the new rule.

• Rule Implementation:
  Added IndentContinuationLineRule, IndentContinuationLineOptions, and supporting logic in src/lint/rules/indentation.rs.
  The rule checks for correct indentation of continuation lines in statements and object contents.
  Integrated the rule into the CurrentRules struct and rule instantiation logic.

• Integration:
  Updated TreeElement implementations for statements and DML objects to call the new rule.
  Adjusted imports and function signatures as needed to support the new logic.

• Tests:
  Added comprehensive tests in src/lint/rules/tests/indentation/continuation_line.rs for both correct and incorrect cases.

• Refactoring
  Refactored some token filtering logic for parenthesized expressions to facilitate rule implementation.

[jvsqzj]

I've included this commit in PR #109 for branch feature/73-line-breaking

@me-cr you can close this PR and we will integrate this as part of Line Length rules.