Add :eval_generated filter for ignore_branches and ignore_methods

[sferik]

Rails delegate (and other module_eval / class_eval / instance_eval macros that pass __FILE__ and __LINE__) inject method and branch entries into a file's coverage data even when the static source has nothing at that line. Ruby's Coverage library attributes the eval'd code to the caller's position, so a single delegate call shows up as a missed def and a missed if branch wherever the macro fires. The previous workaround was to disable eval coverage entirely, which loses the legitimate signal.

Adds the :eval_generated token to SimpleCov.ignore_branches and adds a new SimpleCov.ignore_methods with the same token. Both filters walk the static source through SimpleCov::StaticCoverageExtractor (Prism) and drop any Coverage tuple whose start line lacks a real def keyword (for methods) or branch construct (for branches). Line presence is the matcher, so a real branch or def that shares a line with an eval-generated entry survives. Prism ships with Ruby 3.3+, and on older Rubies gem install prism enables the filter, otherwise the setting is a no-op.

The filters are opt-in and stored regardless of which coverage criteria are enabled at call time, matching the existing ignore_branches lifecycle. Unknown tokens raise SimpleCov::ConfigurationError to catch typos. README and CHANGELOG updated, with specs covering the DSL, the new StaticCoverageExtractor.real_source_positions helper, and SourceFile integration.