EPUB parsing optimizations

[chocolatkey]

AI was tasked with benchmarking (using built-in Go testing framework) the EPUB parsing, to try and find potential optimizations. This is the result. The main "optimization" left I'm not touching any time soon is the XML parsing done by xmlquery

[Copilot]

Pull request overview

This PR focuses on improving EPUB parsing performance by reducing redundant work (notably around encryption.xml parsing), streamlining whitespace handling, adding a benchmark harness, and optimizing ZIP archive entry lookups.

Changes:

• Extend protection.IdentifyEPUBProtection to optionally return a parsed encryption.xml document so callers can reuse it instead of re-parsing.
• Replace regex-based whitespace normalization with strings.Fields / a custom ASCII whitespace collapser, and remove a few redundant computations.
• Add an EPUB parser benchmark and speed up ZIP entry lookup via a lazily-built name index.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
pkg/protection/epub.go	Changes DRM detection to probe known paths via Get()+Length(), and returns an optional parsed encryption.xml document.
pkg/protection/epub_test.go	Updates tests for the new IdentifyEPUBProtection return signature.
pkg/parser/epub/property_data_type.go	Simplifies property tokenization and introduces collapseWhitespace to replace regex usage.
pkg/parser/epub/parser.go	Reuses the encryption.xml document from protection detection to avoid re-reading/re-parsing in some cases.
pkg/parser/epub/parser_test.go	Updates encryption parsing test to pass through the optional document.
pkg/parser/epub/parser_packagedoc.go	Avoids re-parsing the same properties attribute value twice.
pkg/parser/epub/parser_ncx.go	Switches title normalization to collapseWhitespace.
pkg/parser/epub/parser_navdoc.go	Switches title normalization to collapseWhitespace and tweaks href defaulting logic.
pkg/parser/epub/parser_bench_test.go	Adds a benchmark that parses EPUBs found in a local publications directory.
pkg/archive/archive_zip.go	Adds a lazily-built cleaned-path index for O(1) ZIP entry lookup and shares entry wrappers via sync.Map.

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