support http 1 and 2

[lazarusA]

closes #11

[gemini-code-assist]

Code Review

This pull request introduces compatibility abstractions to support both HTTP 1.x and 2.x, defines a new ZarrServer struct with associated management functions, and updates the browzarr entry point and tests accordingly. The review feedback highlights three critical issues: a potential MethodError in start_browzarr when port is nothing, an inefficient file-reading mechanism in serve_zarr that could lead to out-of-memory errors on large Zarr chunks, and an unnecessary memory read of existing .zmetadata files that triggers misleading logs.

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