feat: add pred(callable) — first-class predicate pattern

[Copilot]

Adds pred(callable) as a first-class pattern that lifts an arbitrary unary predicate into the match phase, avoiding the need for post-bind guards (pattern[guard]) when no binding is required.

Changes

• include/ptn/pattern/pred.hpp — New pred_pattern<Callable> CRTP type + pred() factory. Non-binding (empty binding_args), consistent with wildcard, any/all, etc.
• include/ptn/patternia.hpp — Includes pred.hpp; exports ptn::pred.
• CMakeLists.txt — Adds pred.hpp to PTN_HEADERS.
• tests/tests_pred_pattern.cpp — 10 tests: match/fallback, string subjects, composition with any/all, reuse, PTN_ON macro, fully-qualified usage.
• tests/CMakeLists.txt — Wires in the new test TU.
• docs/roadmap.md — Promotes pred(callable) from WIP → FINISHED (v0.9.3).

Usage

match(x) | on(
  pred([](int v) { return v % 2 == 0; }) >> "even",
  _ >> "odd"
);

// Composes natively with any()/all()
match(x) | on(
  all(pred([](int v) { return v > 0; }),
      pred([](int v) { return v % 2 == 0; })) >> "positive even",
  _ >> "other"
);

[Copilot]

Pull request overview

Adds a new first-class pred(callable) pattern to Patternia, enabling match-time evaluation of unary predicates as non-binding patterns (usable in on(...) and composable with any/all), along with build/test/docs wiring.

Changes:

• Introduces include/ptn/pattern/pred.hpp implementing pred_pattern<Callable> and the pred() factory (non-binding).
• Exports ptn::pred via the umbrella header and registers the header in CMake.
• Adds a dedicated GTest TU and wires it into the tests build; updates the roadmap status.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
include/ptn/pattern/pred.hpp	New predicate pattern implementation + binding contract specialization.
include/ptn/patternia.hpp	Includes pred.hpp and exports ptn::pred in the public API.
CMakeLists.txt	Adds the new public header to PTN_HEADERS.
tests/tests_pred_pattern.cpp	New unit tests covering basic matching and composition scenarios.
tests/CMakeLists.txt	Adds the new test translation unit to ptn_tests.
docs/roadmap.md	Marks pred(callable) as finished and references a new release entry.

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[Copilot]

pred_pattern::match calls the stored callable via fn(...), which prevents using certain valid “callable” forms such as pointers-to-member functions/data members. If the intent is to lift any unary predicate, consider using std::invoke(fn, subj) (and include <functional>) so member pointers and std::reference_wrapper work as expected.

[Copilot]

This roadmap entry links to changelog/v0.9.3.md, but that file doesn’t exist in docs/changelog/ (latest present is v0.9.2.md). Either add the v0.9.3 changelog file in this PR or change the link/text to reference an existing release to avoid a broken docs link.

Suggested change

	Completed in [v0.9.3](changelog/v0.9.3.md):
	Completed in v0.9.3: