feat: Addressables REST module for hot-update asset management

[ShutovKS]

Summary

Adds an optional reflection-based Addressables REST module, validated against com.unity.addressables 3.1.0 without a hard assembly dependency.

Endpoints

• addressables_check_installed
• addressables_group_list
• addressables_group_create
• addressables_group_delete
• addressables_group_add_entry
• addressables_profile_get
• addressables_profile_set
• addressables_build

Addressables 3.1 compatibility

• Resolves IsDefaultGroup() correctly and also verifies settings.DefaultGroup.
• Reads group entries through ICollection.
• Resolves the six-parameter CreateGroup overload.
• Creates groups with BundledAssetGroupSchema and ContentUpdateGroupSchema.
• Resolves BuildPlayerContent(out result) and surfaces result.Error.
• Reports the UPM package version through PackageInfo.FindForAssembly.
• Refuses to delete the default group.

Verification

• Unity 6000.3.11f1 + Addressables 3.1.0 full EditMode: 220/220 passed.
• Real endpoint test creates a group, verifies both schemas, adds an addressed asset, builds content, and verifies catalog and bundle output.
• Installed version assertion returns 3.1.0.
• git diff --check: passed.

[Copilot]

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[Besty0728]

Okay, I'll review your PR when I have time.

[Besty0728]

Tested in Unity 6.3 LTS against Addressables 3.1.0. The direction is useful, but this is not merge-ready. Current reflection assumes APIs that do not match 3.1.0: IsDefaultGroup is a method, entries is not IList, CreateGroup needs the params Type[] argument, and BuildPlayerContent has multiple overloads. In real execution, group_create and build fail, entryCount/default flags are wrong, version reports 0.0.0.0, and group_delete was able to delete Default Local Group. Please correct the reflection bindings, make default-group protection reliable, and add endpoint tests against a supported Addressables version.

[ShutovKS]

Review fixes are now on this PR branch only (head 58ad1bd).

• Correct Addressables 3.1 reflection bindings.
• New groups include BundledAssetGroupSchema and ContentUpdateGroupSchema.
• Build result errors are inspected and surfaced.
• Package version comes from UPM PackageInfo (3.1.0).
• Default-group deletion is protected.
• Added a real endpoint test that creates a group, adds an addressed asset, builds content, and verifies catalog/bundle output.

Verification on Unity 6000.3.11f1 + Addressables 3.1.0: full EditMode 220/220 passed; real content build test 1/1 passed; git diff --check passes.