chore: migrate java-storage-nio to monorepo

[suztomo]

b/477663567

=> #12311

[gemini-code-assist]

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[suztomo]

Error: Failed to execute goal org.apache.maven.plugins:maven-enforcer-plugin:3.5.0:enforce (enforce) on project google-cloud-nio: Error: Rule 0: org.apache.maven.enforcer.rules.dependency.RequireUpperBoundDeps failed with message:
Error: Failed while enforcing RequireUpperBoundDeps. The error(s) are [
Error: Require upper bound dependencies error for com.google.apis:google-api-services-storage:v1-rev20251118-2.0.0 paths to dependency are:
Error: +-com.google.cloud:google-cloud-nio:0.128.14
Error: +-com.google.apis:google-api-services-storage:v1-rev20251118-2.0.0
Error: and
Error: +-com.google.cloud:google-cloud-nio:0.128.14
Error: +-com.google.cloud:google-cloud-storage:2.64.1
Error: +-com.google.apis:google-api-services-storage:v1-rev20251118-2.0.0 (managed) <-- com.google.apis:google-api-services-storage:v1-rev20260204-2.0.0
Error: ]
Error: -> [Help 1]

[suztomo]

The generation-diff check failed: https://github.com/googleapis/google-cloud-java/actions/runs/23751682664/job/69195206283?pr=12295

+ <dependency>
+ <groupId>com.google.cloud</groupId>
+ <artifactId>google-cloud-nio-bom</artifactId>
+ <version>0.128.14</version><!-- {x-version-update:google-cloud-nio:current} -->
+ <type>pom</type>
+ <scope>import</scope>
+ </dependency>

The artifact is currently imported in google-cloud-bom: https://github.com/googleapis/java-cloud-bom/blob/e2c2207ea0b528a7a478b307eb2a33a100e3b66f/google-cloud-bom/pom.xml#L195. So adding it there shouldn't be a problem.

[suztomo]

I'll create from a branch within this repository to avoid generation-diff.