Upgrade lexical-core to 0.8

[Dandandan]

Which issue does this PR close?

Closes #747

Rationale for this change

Upgrade to latest version, which has some performance improvements (usage of Eisel-Lemire algorithm being one important change)

See:
https://github.com/Alexhuszagh/rust-lexical/releases/tag/v0.8.0

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #748 (1e9dae2) into master (3b56485) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #748   +/-   ##
=======================================
  Coverage   82.47%   82.47%           
=======================================
  Files         168      168           
  Lines       47715    47715           
=======================================
  Hits        39353    39353           
  Misses       8362     8362           

Impacted Files	Coverage Δ
arrow/src/compute/kernels/boolean.rs	96.76% <ø> (ø)

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