fix(scenario): warn when selected attack techniques have no registered factory

[fei (feiiiiii5)]

Description

resolve_technique_factories() in pyrit/scenario/core/matrix_atomic_attack_builder.py silently dropped selected techniques whose factory is not registered — the docstring even documented the behavior as "silently dropped". When a scenario (or a user of extra_factories) selects a technique that was never registered, e.g. due to a typo or a custom technique added under a different name, the run quietly proceeds with fewer attacks and there is no signal anywhere that selections were discarded.

This PR emits a single warning naming every missing technique, then proceeds with the remaining ones as before:

WARNING  pyrit.scenario.core.matrix_atomic_attack_builder:matrix_atomic_attack_builder.py:171 Skipping 2 selected attack technique(s) with no registered factory: missing_a, missing_b. Register the technique(s) (or pass them via extra_factories) to include them in the run.

Design notes:

• Warning, not an exception: dropping is intentional fallback behavior (per the original docstring), and callers may legitimately probe which techniques are available; this only makes it observable. Happy to switch to raising if maintainers prefer strictness.
• One aggregated warning per call, names deduplicated but kept in selection order, so repeated selections don't spam the log.

Fixes #2461

Tests

Added three regression tests to TestResolveTechniqueFactories:

• warning is emitted when a selected technique has no factory, and names it
• no warning when all selected techniques resolve
• one warning listing each distinct missing name once, in selection order (deduplicated)

All 35 tests in tests/unit/scenario/core/test_matrix_atomic_attack_builder.py pass locally (73 failed / 569 passed elsewhere in tests/unit/scenario/ is identical to the pre-change baseline on this machine — those failures are environment-only, unrelated modules). Ruff check + format pass on both touched files.