Delay reading of vba project

[sftse]

Supersedes #572

[sftse]

Not sure what the rules of semantic versioning say about functions that are not callable but manage to be visible. VbaProject::from_cfb appears in the public documentation but is not callable because Cfb is not pub. This PR makes it pub(crate).

[jmcnamara]

This PR makes it pub(crate).

+1. It was unnecessarily public. I dropped it completely in my cfb.rs PR and just used VbaProject::new().

[jmcnamara]

I have no major comments on this. Overall it looks very good. I'll try do a full review in a few days.

In the meantime I'll kick off copilot. Just ignore/resolve any irrelevant comments.

[Copilot]

Pull Request Overview

This PR refactors the VBA project API to simplify error handling and ownership semantics. The main change converts vba_project() from returning Option<Result<Cow<'_, VbaProject>, Error>> to Result<Option<VbaProject>, Error>, eliminating the Cow wrapper and inverting the Option/Result nesting for more idiomatic Rust error handling.

Key changes:

• Changed vba_project() signature from Option<Result<Cow<'_, VbaProject>, Error>> to Result<Option<VbaProject>, Error> across all workbook types
• Removed redundant XmlAttribute error variant in XlsxError, consolidating it with existing XmlAttr variant
• Refactored Xls to store Cfb and reader internally, enabling lazy VBA loading instead of eager loading
• Updated all test cases and examples to use the new API pattern

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/lib.rs	Updated Reader trait signature for vba_project() and updated documentation example
src/vba.rs	Made from_cfb() internal, updated documentation, and added derive traits to VbaProject
src/xlsx/mod.rs	Removed duplicate XmlAttribute error variant, simplified error handling, and updated vba_project() implementation
src/xlsb/mod.rs	Updated vba_project() implementation and added missing error conversions
src/xls.rs	Refactored to store Cfb and reader for lazy VBA loading, updated vba_project() implementation
src/ods.rs	Updated vba_project() signature (ODS doesn't support VBA) and fixed error conversion
src/cfb.rs	Added derive traits to XlsEncoding and simplified Vec::with_capacity logic
src/auto.rs	Updated vba_project() implementation for auto-detected workbook wrapper
src/xlsx/cells_reader.rs	Simplified error handling by removing redundant map_err calls
tests/test.rs	Updated all test cases to use new VBA API and added VBA reference/module tests
examples/search_errors.rs	Updated to use new VBA API pattern
fuzz/fuzz_targets/fuzz_all.rs	Updated to use new VBA API pattern
README.md	Updated documentation example

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[jmcnamara]

Overall this look good to me. @sftse are you happy to merge?

[sftse]

GTM

[jmcnamara]

Merged. Thanks.