feat: add a rust crate

[lukapeschke]

This allows to use fastexcel from rust. It can be used to generate Fastexcel columns, which are simple wrappers around owned data.

An optional polars extra allows to convert an ExcelSheet or an ExcelTable to a DataFrame.

Different cargo features have been added to distinguish between Python and Rust builds, as we don't need arrow for rust usage (polars ships its own implem when enabled)

See rust integration tests for usage examples

[Fanaen]

Really neat! 🙏

Only a couple minor nitpicks.
My review is rather shallow as I'm not used to this project yet.
Another review would be appreciated!

[Fanaen]

Suggested change

	"Column '{name}' has length {data_len} but expected {len}"
	"column '{name}' has length {data_len} but expected {len}"

[Fanaen]

Case seems different here (uppercase in most src/types/excelreader/mod.rs::ExcelReader)

[PrettyWood]

Very very cool! Looks great overall.
2 main points:

• add rustdoc comments on main structs, methods,...
• API improvement on FastExcelSeries
  Not blocking but would love it :)

[PrettyWood]

add doc

[PrettyWood]

Add doc
I would also impl len() and is_empty + IntoIterator for each variant

[lukapeschke]

In the end, I didn't implement those, because the length of a Null Series cannot be known. I added into_$type methods to access the raw data, and the docs recommend to use FastExcelColumn over FastExcelSeries.

[Copilot]

Pull Request Overview

This pull request adds a Rust crate implementation for fastexcel, enabling usage from Rust code in addition to the existing Python interface. The Rust API provides access to Excel sheet and table data through column-based structures, with optional Polars DataFrame integration.

Key changes include:

• Rust API implementation with FastExcelColumn and FastExcelSeries types
• Optional Polars integration for DataFrame conversion
• Feature-based compilation to separate Python and Rust dependencies
• Restructured codebase to support both Python and Rust usage patterns

Reviewed Changes

Copilot reviewed 34 out of 59 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/lib.rs	Exposes public Rust API and maintains Python module compatibility
src/types/mod.rs	Restructures type exports for both Python and Rust usage
src/data/mod.rs	Implements FastExcelColumn and FastExcelSeries for Rust API
src/types/excelreader/mod.rs	Refactors ExcelReader to support both Python and Rust usage
tests/fastexcel.rs	Adds comprehensive Rust integration tests

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[PrettyWood]

Also readme needs an update

[lukapeschke]

@PrettyWood A second review would be great, sync with main wasn't easy 🙏

In addition to branch update, I did the following:

• Added rust docs & rust doc check to the CI
• Fixed some python typing
• Made the Rust API for Series/Columns nicer
• Updated the README