Replace VarInt.getLength with Protobuf's branchless implementation

[sjvanrossum]

See https://github.com/protocolbuffers/protobuf/blob/0a2f7757e38b07c2e40c5c885a7100e8c16eb40f/java/core/src/main/java/com/google/protobuf/CodedOutputStream.java#L700 for details. This change copies Protobuf's branchless implementation for varint length calculation.

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[gemini-code-assist[bot]]

Summary of Changes

Hello @sjvanrossum, I'm Gemini Code Assist[^1]! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on optimizing the calculation of variable-length integer (VarInt) encoding lengths within the VarInt utility class. By integrating a branchless algorithm derived from Protocol Buffers, the change aims to enhance performance by eliminating conditional jumps and utilizing efficient bitwise operations, resulting in a faster and more streamlined length determination process.

Highlights

• Performance Optimization: Replaced the iterative VarInt.getLength calculation with a branchless, bit-manipulation-based implementation inspired by Google's Protobuf library for both int and long values.
• Code Modernization: Adopted a more efficient and modern approach for varint length calculation, leveraging Integer.numberOfLeadingZeros and Long.numberOfLeadingZeros for improved performance.

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[scwhittle]

Need to fix spotless also