Add CalDAV support

[LuceusXylian]

• Add CalDAV support
• CI: Check build with caldav

[LuceusXylian]

Partially fixes issue #8.

[Copilot]

Pull Request Overview

This PR adds comprehensive CalDAV support to the dav-server library, extending the existing WebDAV functionality with calendar-specific features. CalDAV is a standardized protocol for calendar data management over HTTP, defined in RFC 4791.

• Implements CalDAV methods (MKCALENDAR, REPORT) and calendar-specific WebDAV properties
• Adds iCalendar data validation and calendar query functionality
• Includes comprehensive test coverage and example application
• Makes CalDAV support optional via the "caldav" feature flag

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/caldav_tests.rs	Comprehensive test suite covering CalDAV functionality
src/util.rs	Adds REPORT and MKCALENDAR methods to DavMethod enum
src/lib.rs	Updates documentation and exports CalDAV module
src/handle_props.rs	Extends property handling with CalDAV-specific properties
src/handle_options.rs	Advertises CalDAV capabilities in OPTIONS responses
src/handle_gethead.rs	Adds Nextcloud compatibility and improves HTML output
src/handle_caldav.rs	Core CalDAV request handling implementation
src/davheaders.rs	Extends Depth header enum with Default variant
src/davhandler.rs	Integrates CalDAV methods into main request handler
src/caldav.rs	CalDAV data structures and utility functions
src/body.rs	Makes body types public for external access
src/actix.rs	Minor code improvements and modernizations
examples/caldav.rs	Example CalDAV server implementation
README.CalDAV.md	Comprehensive CalDAV documentation
Cargo.toml	Adds CalDAV dependencies and version bump
.github/workflows/CI.yml	Adds CalDAV feature to CI builds

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[messense]

Thanks!