feat: UNIC-1977 Implement write and insert for ExcelLoader

[Asciax]

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[Copilot]

Pull request overview

This pull request implements write and insert operations for ExcelLoader to support writing Excel files using Spark DataFrames. The implementation fills in previously unimplemented methods (marked with ???) and upgrades the spark-excel dependency to a more actively maintained version.

Changes:

• Implemented write, writeOnce, and insert methods in ExcelLoader using Spark's SaveMode.Overwrite and SaveMode.Append
• Integrated ExcelLoader with LoadResolver for OverWrite and Insert load types
• Upgraded spark-excel dependency from "com.crealytics" to "dev.mauch" (version 3.5.5_0.30.2)

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 5 comments.

File	Description
datalake-spark3/src/main/scala/bio/ferlab/datalake/spark3/loader/ExcelLoader.scala	Implements write, writeOnce, and insert methods with schema validation
datalake-spark3/src/main/scala/bio/ferlab/datalake/spark3/loader/LoadResolver.scala	Adds EXCEL format support for OverWrite and Insert load types
datalake-spark3/src/test/scala/bio/ferlab/datalake/spark3/loader/ExcelLoaderSpec.scala	Adds comprehensive test coverage for write and insert operations with cleanup utilities
build.sbt	Updates spark-excel dependency to newer maintained fork

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