General refactor and housekeeping

[ferenc-csaky]

Relevant changes

• Added a shorthand for every CLI argument and updated README accordingly.
• Refactored the environment variable handling utility, and moved all relevant logic into EnvVarUtils class.
• Replaced assertions to AssertJ in every test file.

[Copilot]

Pull Request Overview

This PR performs a general refactor and cleanup across the codebase, adding shorthand CLI flags, centralizing environment‐variable logic, and standardizing test assertions.

• Add short (-p, -s, -c, -u, -m) options for all command‐line arguments and update README.
• Move all environment‐variable parsing into a single EnvVarUtils class and introduce JSON support.
• Replace JUnit5 Assertions calls with AssertJ in every test.

Reviewed Changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated no comments.

File	Description
README.md	Updated CLI argument table, added shorthand flags, bumped version
flink-sql-runner/src/main/java/com/datasqrl/EnvVarUtils.java	Extracted and improved env var resolution logic, added JSON support
flink-sql-runner/src/main/java/com/datasqrl/FlinkMain.java / SqlExecutor.java / JsonEnvVarDeserializer.java	Switched to EnvVarUtils methods and removed old helpers
All test files (various under src/test/java)	Migrated from JUnit assertions to AssertJ for consistency

Comments suppressed due to low confidence (2)

flink-sql-runner/src/test/java/com/datasqrl/SqlRunnerTest.java:36

• In setUp(), udfPath is never initialized before being used in the CLI args array, resulting in a null argument. Either initialize udfPath to a valid path or remove the --udfpath flag from the test arguments.

private String udfPath;

flink-sql-runner/src/main/java/com/datasqrl/EnvVarUtils.java:55

• [nitpick] Consider using StringBuilder instead of the synchronized StringBuffer here, since this method is single-threaded and will have better performance.

var res = new StringBuffer();

[velo]

LGTM.

Not sure if you used this:
https://docs.openrewrite.org/recipes/java/testing/assertj/assertj-best-practices

[ferenc-csaky]

LGTM.

Not sure if you used this: https://docs.openrewrite.org/recipes/java/testing/assertj/assertj-best-practices

Nope, coding agent and myself, but most asserts are pretty straightforward so not much room for AssertJ goodness (yet).