feat: f() gotemplate cel function

[adityathebe]

resolves: #128

[Copilot]

Pull Request Overview

Implements a new CEL function f() that enables GoTemplate functionality within CEL expressions. This allows CEL to process template strings with both $() and {{}} delimiters using the existing GoTemplate engine.

Key changes:

• Added new CEL function f() that accepts a format string and data object
• Added comprehensive test coverage for the new functionality
• Reorganized imports for better structure

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
cel.go	Implements the new f() CEL function with GoTemplate integration and data handling logic
tests/cel_test.go	Adds test cases for the new GoTemplate CEL function and reorganizes imports

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