Rust Binder: Replace List in `context.rs` with Vec

[Darksonn]

Currently the context.rs file uses List to store the global list of contexts. This has the disadvantage that calls to remove are unsafe.

To get rid of these unsafe operations, the List should be replaced with a KVVec.

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This requires submitting a proper patch to the LKML and the Rust for Linux mailing list. Please recall to test your changes (including generating the documentation if changed, running the Rust doctests if changed, etc.), to use a proper title for the commit, to sign your commit under the Developer's Certificate of Origin and to add a Suggested-by: tag, and a Link: tag to this issue. Please see https://docs.kernel.org/process/submitting-patches.html and https://rust-for-linux.com/contributing for details.

[DoobyDoPap]

Hey @Darksonn , I would like to take this issue.