ci: avoid shellexpand in lance-io

[lance-community]

Link to failing workflow run: https://github.com/lance-format/lance/actions/runs/22272601908/job/64429623103?pr=5980

Summary of failures:

• linux-build failed compiling shellexpand 3.1.1 on nightly (llvm-cov) with E0308 mismatched types.

Fixes applied:

• Replaced shellexpand tilde expansion in lance-io with a local helper using the home crate.
• Dropped the shellexpand dependency and added home to workspace and lance-io dependencies.
• Updated Cargo.lock accordingly.

[github-actions]

PR Review: ci: avoid shellexpand in lance-io

Summary: This PR replaces the shellexpand crate with a local expand_tilde helper using the home crate to fix nightly compilation failures.

P1 - Missing Unit Tests for expand_tilde

The new expand_tilde function at rust/lance-io/src/object_store.rs:356 handles critical path expansion logic but lacks dedicated unit tests. While test_tilde_expansion provides integration coverage for ~/path, consider adding unit tests for edge cases:

• ~ alone (just home dir)
• ~\path (Windows separator)
• Non-tilde paths (passthrough)
• home_dir() returning None (fallback behavior)

This is particularly important since path handling is security-sensitive and the function has subtle logic around separator handling.

Minor Observation

The implementation correctly drops support for ~username expansion (resolving other users' home directories), which shellexpand may have supported. This appears intentional and acceptable since Lance likely never relied on that feature - the existing test only covers ~/path.

---

Overall the fix is reasonable. The implementation looks correct for the supported use cases (~ and ~/path).

[codecov]

Codecov Report

❌ Patch coverage is 73.68421% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
rust/lance-io/src/object_store.rs	73.68%	3 Missing and 2 partials ⚠️

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