Add datafusion-rocksdb crate with basic layout and README

[Copilot]

Plan for adding datafusion-rocksdb crate:

• Explore repository structure and understand existing crate patterns
• Verify build and test process works
• Create datafusion-rocksdb crate directory structure
• Add Cargo.toml for datafusion-rocksdb crate
• Add README.md for datafusion-rocksdb crate
• Create basic lib.rs with module structure
• Verify the new crate builds successfully
• Run final tests to ensure no regressions
• Fix CI to use project-specific Rust toolchain version
• Update Rust toolchain to 1.86.0 for cargo-machete compatibility

Original prompt

Create a branch adding a new crate datafusion-rocksdb. This crate will provide udfs and datafusion extension points. Start with just adding the general layout and readme

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[matthewmturner]

@copilot Can you include a fix for CI. Looks like rust toolchain needs to be updated

[Copilot]

@copilot Can you include a fix for CI. Looks like rust toolchain needs to be updated

Fixed in commit a7520aa - removed the override to stable toolchain so CI now uses the version specified in rust-toolchain.toml (1.85.0).

@copilot Can you include a fix for CI. Looks like rust toolchain needs to be updated

Fixed in commit a7520aa - removed the override to stable toolchain so CI now uses the version specified in rust-toolchain.toml (1.85.0).

[matthewmturner]

@copilot CI is still failing, fix it. this is one of the errors i saw - we can increase the rust toolchain version if needed

Compiling just v1.43.0
Finished release profile [optimized] target(s) in 1m 06s
Installing /usr/local/cargo/bin/just
Installed package just v1.43.0 (executable just)
error: failed to compile cargo-machete v0.9.1, intermediate artifacts can be found at /tmp/cargo-installTH94TX.
To reuse those artifacts with a future compilation, set the environment variable CARGO_TARGET_DIR to that path.

Caused by:
rustc 1.85.0 is not supported by the following packages:
cargo-util-schemas@0.8.2 requires rustc 1.86
cargo_metadata@0.21.0 requires rustc 1.86.0
Try re-running cargo install with --locked
Summary Successfully installed just! Failed to install cargo-machete (see error(s) above).
error: some crates failed to install

[Copilot]

@copilot CI is still failing, fix it. this is one of the errors i saw - we can increase the rust toolchain version if needed

Compiling just v1.43.0
...

Updated Rust toolchain to 1.86.0 in commit to fix cargo-machete installation. The crates cargo-util-schemas@0.8.2 and cargo_metadata@0.21.0 both require Rust 1.86.