feat(flow): impl ScalarExpr&Scalar Function

[discord9]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

Add impl for ScalarExpr&Scalar Functions

Please explain IN DETAIL what the changes are in this PR and why they are needed:

• Added impl code which eval Unary, Binary and Variadic Func

• Added utilty functions for ScalarExpr like get supporting(column being used in expression) column for a ScalarExpr.

• Most importantly, added utility functions for Temporal Filter, which can extract bounding condition including now() function and comparsion expression and express sliding windows etc.

• Summarize your change (mandatory)
  useful methods for Scalar Expr, and eval method for Scalar function

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Attention: 296 lines in your changes are missing coverage. Please review.

Comparison is base (c62c67c) 85.64% compared to head (f721059) 85.13%.
Report is 46 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3283      +/-   ##
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- Coverage   85.64%   85.13%   -0.52%     
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  Files         865      884      +19     
  Lines      140798   144751    +3953     
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+ Hits       120593   123228    +2635     
- Misses      20205    21523    +1318     

[tisonkun]

nit: add a "flow" scope in the PR title (a.k.a. feat(flow)). It "shocks" me that we don't implement ScalarExpr for GreptimeDB, XD.

[zhongzc]

LGTM