V3 lockfiles

[vinnybod]

Integrates these two upstream changes that are not yet merged to master
bazel-contrib#1454
bazel-contrib#1500

[Copilot]

Pull request overview

This PR integrates V3 lockfile format support by updating the lockfile version from "2" to "3" and refactoring hash calculation to use per-artifact hashes instead of a single aggregate hash. The key changes enable more granular dependency tracking and better change detection.

• Updates lockfile format version from "2" to "3" across all test fixtures and production code
• Refactors hash calculation to compute individual hashes for each artifact and repository instead of a single aggregate hash
• Adds support for both V2 and V3 lockfile formats with migration path

Reviewed changes

Copilot reviewed 24 out of 24 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/unit/coursier_test.bzl	Adds assertion to verify excluded artifacts affect hash calculation
tests/integration/pom_file/*.golden.xml	Adds golden files for new POM generation test scenarios
tests/integration/pom_file/BUILD	Adds comprehensive tests for transitive dependencies with exclusions in POMs
tests/custom_maven_install/*.json	Updates all lockfiles to V3 format with per-artifact hashes
tests/com/github/bazelbuild/rules_jvm_external/resolver/lockfile/V3LockFileTest.java	Renames test class from V2 to V3 and adds hash validation test
tests/com/github/bazelbuild/rules_jvm_external/resolver/lockfile/BUILD	Updates test configuration for renamed test class
private/tools/java/.../V3LockFile.java	Renames class from V2LockFile to V3LockFile and updates version string
private/tools/java/.../ResolverConfig.java	Changes input hash from String to Map and updates CLI argument handling
private/tools/java/.../AbstractMain.java	Completely refactors hash calculation to compute per-artifact hashes with dependency tracking
private/tools/java/.../LockFileConverter.java	Updates reference from V2LockFile to V3LockFile
private/rules/v3_lock_file.bzl	Renames from v2_lock_file.bzl and adds V3 hash computation logic with dependency-aware hashing
private/rules/pin_dependencies.bzl	Updates to write input hash to separate JSON file instead of passing as command-line argument
private/rules/maven_utils.bzl	Removes validation that prevented exclusions on transitive dependencies
private/rules/coursier.bzl	Updates hash signature computation to return per-artifact hashes and adds V3 lockfile support
private/extensions/maven.bzl	Adds V3 lockfile format detection and imports
maven_install.json	Updates root lockfile to V3 format
BUILD	Exports maven_install.json for use in tests

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