Release 0.12.0

This release adds XML as a first-class data format for catalog entries and extends the internal coverage analytics pipeline.

What's New

XML Extension: You can now read and write XML data in your catalog using Flowthru.Extensions.Xml. XmlItemFactory.Single.Xml<T>() creates a catalog entry backed by a single XML file, and ItemFactory.Enumerable.XmlDocuments<T>() reads all *.xml files in a directory, yielding each as an XmlDocument<T> that carries the source file name. Files follow System.Xml.Serialization conventions — decorate your schema type with [XmlRoot], [XmlElement], and [XmlAttribute] as you normally would.
- FlowthruCoverage Example: A new advanced example demonstrates reading a directory of Cobertura XML coverage reports, processing them through a multi-stage pipeline, and generating a Python-based coverage heatmap. See FlowthruCoverage.

Template Testing Stability: Template integration tests had intermittent failures under certain build conditions. These tests now run more reliably.
Test Output Caching: A cache key issue caused stale test outputs to be used in some scenarios. This is resolved.
FUnit Discovery in Examples: The examples project was incorrectly being scanned for FUnit tests, which produced spurious discovery results. Discovery is now scoped correctly.

remove funit discovery from examples project (11b41d80)
code coverage for examples (27f468b4)
resolve test output cache issue (c8d6a965)
better coverage analytics (5858b558)
less flakey template testing (f94a8de7)
updated inputs for coverage (d0646912)
unignore missing coverage analysis flow (d9f2d7cb)