Fix copyright header placement in IndexMetadata and LSMVectorIndexMetadata

[Copilot]

What does this PR do?

Fixes copyright header placement in IndexMetadata.java and LSMVectorIndexMetadata.java. Headers were incorrectly placed after the package statement and imports. Now follows standard Java convention with headers at file start, including SPDX identifiers.

Motivation

Addresses feedback from PR #2828 code review regarding improper copyright header positioning.

Related issues

• Parent PR: #2828
• Review comment: https://github.com/ArcadeData/arcadedb/pull/2828#discussion_r2560654076

Additional Notes

Both files now match the standard format used throughout the codebase:

• Copyright header at file start
• SPDX-FileCopyrightText and SPDX-License-Identifier included
• Package statement follows header
• Imports follow package

Checklist

• [ ] I have run the build using mvn clean package command
• [ ] My unit tests cover both failure and success scenarios

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