POC: make Delta Kernel core target-safe for browser WASM

[ethan-tyler]

Tracks daxis-io/axon#2.

This clean candidate keeps native defaults intact while making the Arrow-backed synchronous engine constructible on wasm32-unknown-unknown with an explicitly prefetched object store. It removes browser read-path entropy and cloud-provider batteries, keeps filesystem URL helpers off the browser target, and adds a standalone exact-target dependency-policy proof.

The audit correction at c9a475f3394adc5296c4f16587c1f69c6e87213e preserves requested byte ranges by delegating to ObjectStore::get_range and replaces the copy_atomic panic with a typed Unsupported error.

Verification:

• 10 focused storage tests pass.
• The native nextest suite passes 7,432 tests with 20 skipped.
• Native all-feature check and exact target profiles pass.
• Corrected browser stack CI: https://github.com/daxis-io/delta-kernel-rs/actions/runs/30183035000

The Daxis-only stack branch pins immutable Arrow and object_store revisions separately; those pins are intentionally absent here. This remains a draft POC PR against the immutable compatibility base.

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Title: POC: make Delta Kernel core target-safe for browser WASM
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Title: POC: make Delta Kernel core target-safe for browser WASM
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Title: POC: make Delta Kernel core target-safe for browser WASM
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Title: POC: make Delta Kernel core target-safe for browser WASM
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Title: POC: make Delta Kernel core target-safe for browser WASM
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Title: POC: make Delta Kernel core target-safe for browser WASM
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Title: POC: make Delta Kernel core target-safe for browser WASM