Print the active section/generator selection

Description

When a section/generator selection (-c/--section, -g/--generator-index, or -p/--path-filter) is in effect, the console and compact reporters now print the active path filters on a Path filters: line, right below the existing Filters: line and using the same highlight colour:

Filters: "foo"
Path filters: c:"A" g:0

Section filters are serialized as c:"<filter>" and generator filters as g:<filter>, mirroring the -p/--path-filter syntax. The line is only printed when path filters are present, so default runs are unaffected.

The motivation: Catch2 currently gives no feedback about what was actually selected, which makes it hard to tell what went wrong when a filter combination ends up running no assertions, e.g.:

Filters: "Scenario: Create and train model on entire dataset"
Randomness seeded to: 3221299838
===============================================================================
test cases: 1 | 1 passed
assertions: - none -

Implementation notes:

• Added a serializePathFilters() helper in catch_reporter_helpers, alongside the existing serializeFilters().
• Wired it into ConsoleReporter::testRunStarting and CompactReporter::testRunStarting.
• Documented the printout in docs/filtering-execution-path.md.
• Tests: a unit test for serializePathFilters (format + ordering) and two CTest integration tests verifying both reporters emit the line. Baselines were updated to account for the new self-test case.

Structured reporters (XML/JSON/JUnit/TAP/SonarQube) are intentionally left out of scope; this could be a follow-up if desired.

GitHub Issues

Implements the request in #3099.