feat(chunking): support Split/Splice in bb print

[tyler-french]

This is needed to run bb print to see Split/Splice calls, to test bazelbuild/bazel#28437

BB print just reads the grpc log directly from whats in this file, so updating this file is sufficient.

[Copilot]

Pull request overview

This PR adds support for logging SplitBlob and SpliceBlob RPC calls in the remote execution log proto, enabling the bb print command to display these chunking-related operations. This is needed to test the Split/Splice functionality referenced in the linked Bazel PR.

Changes:

• Added two new proto message types (SplitBlobDetails and SpliceBlobDetails) to capture request/response details for chunking operations
• Extended the RpcCallDetails oneof to include the new message types with field numbers 15 and 16

Comments suppressed due to low confidence (2)

proto/remote_execution_log.proto:127

• There is an extra blank line here that deviates from the consistent spacing pattern used throughout the rest of this proto file. The standard convention is to have a single blank line between message definitions, but this adds two blank lines. Remove one blank line to maintain consistency with the rest of the file.
  proto/remote_execution_log.proto:140
• There is an extra blank line here that deviates from the consistent spacing pattern used throughout the rest of this proto file. The standard convention is to have a single blank line between message definitions, but this adds two blank lines. Remove one blank line to maintain consistency with the rest of the file.

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