fix: upgrade ethnum 1.5.2 to 1.5.3 and unpin nightly toolchain

[LuciferYang]

Summary

Upgrade transitive dependency ethnum from 1.5.2 to 1.5.3 and revert the nightly toolchain pin from #6570.

Dependency chain: lance-arrow → jsonb 0.5.6 → ethnum 1.5.3

Root Cause

ethnum 1.5.2 used unsafe { mem::transmute(()) } to construct TryFromIntError, which broke on nightly > 2026-04-16 when TryFromIntError grew from 0 to 1 byte on Linux x86_64.

ethnum 1.5.3 (nlordell/ethnum-rs#58) replaced all transmute with safe stdlib operations, so the pin is no longer needed.

Test plan

• Verified ethnum 1.5.3 compiles on nightly-2026-04-18 (the version that broke 1.5.2) in Docker Linux x86_64
• linux-build job should pass with unpinned nightly

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[LuciferYang]

error: unresolved link to `create_deletion_mask`
   --> rust/lance/src/index/prefilter.rs:217:16
    |
217 |     /// Like [`create_deletion_mask`] but also restricts results to the given
    |                ^^^^^^^^^^^^^^^^^^^^ no item named `create_deletion_mask` in scope
    |
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
    = note: `-D rustdoc::broken-intra-doc-links` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(rustdoc::broken_intra_doc_links)]`

error: could not document `lance`
warning: build failed, waiting for other jobs to finish...
Error: Process completed with exit code 101.

The failure is unrelated to this PR and has try to fix in #6579

[LuciferYang]

cc @jackye1995

[jackye1995]

looks like there is a rustdoc fix needed, could you fix along the way? 🙏

[LuciferYang]

Thanks for your review. @jackye1995 The doc fix has been merged: #6579

[LuciferYang]

Thank you @Xuanwo