[AURON #1473] Rename module spark-extension-shims-spark3 to spark-extension-shims-spark.

[slfan1989]

Which issue does this PR close?

Closes #1473.

We plan to introduce support for Spark 4. Currently, the module name spark-extension-shims-spark3 is tightly coupled with Spark 3-specific versions. To make the module naming more general and version-agnostic, we should rename it to spark-extension-shims-spark.

This change will make it easier to extend support for multiple Spark versions (e.g., Spark 3.x, Spark 4.x) without duplicating shim module definitions.

Rationale for this change

The local compilation passes.

[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary for Apache Auron Parent Pom 7.0.0-SNAPSHOT:
[INFO] 
[INFO] Apache Auron Parent Pom ............................ SUCCESS [  2.009 s]
[INFO] Apache Auron Proto ................................. SUCCESS [ 13.495 s]
[INFO] Apache Auron Hadoop Shim 2.12 ...................... SUCCESS [  4.903 s]
[INFO] Apache Auron Core .................................. SUCCESS [  7.310 s]
[INFO] Apache Auron Common 2.12 ........................... SUCCESS [  7.611 s]
[INFO] Apache Auron Spark Version Annotation Macros 2.12 .. SUCCESS [  6.020 s]
[INFO] Apache Auron Spark UI 2.12 ......................... SUCCESS [  4.335 s]
[INFO] Apache Auron Spark Extension 2.12 .................. SUCCESS [ 24.360 s]
[INFO] Apache Auron Spark Extension Shims Spark 3.5.7_2.12  SUCCESS [ 18.153 s]
[INFO] Apache Auron Assembly .............................. SUCCESS [  9.452 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  01:38 min
[INFO] Finished at: 2025-10-20T11:30:21+08:00
[INFO] ------------------------------------------------------------------------

What changes are included in this PR?

Rename spark-extension-shims-spark3 to spark-extension-shims-spark.

Are there any user-facing changes?

No.

How was this patch tested?

CI

[slfan1989]

@richox Could you please help review this PR? Thank you very much!

[richox]

as we are using scala-paradise for conditional compiling with different spark version now, the shim package can be further merged into spark-extension module in the future.

[slfan1989]

as we are using scala-paradise for conditional compiling with different spark version now, the shim package can be further merged into spark-extension module in the future.

@richox Thank you for your explanation! This approach makes sense to me as it effectively avoids code duplication and is a good optimization.

[slfan1989]

@cxzl25 @richox Could we merge this PR to proceed with the compatibility development for Spark 4? Thanks a lot.

[slfan1989]

@cxzl25 @richox @turboFei Thank you very much for reviewing the code!