Remediate Ε-W3-T1 package-compat-fixtures review findings

Freeze *.rsbank as binary via .gitattributes; add a truncated additive_forward fixture proving the exact-size proof beats TooNew; enumerate the fixture dir to catch orphaned files; make fixture-size checks fatal instead of just logged; pin fixture version asserts as literals, not build-relative.

CMakeLists.txt

@@ -85,6 +85,7 @@ set(LICE_SRC
 # ---------------------------------------------------------------------------
 set(REASAMPLER_SRC_DIR   ${CMAKE_CURRENT_SOURCE_DIR}/src)
 set(REASAMPLER_TESTS_DIR ${CMAKE_CURRENT_SOURCE_DIR}/tests)
+set(REASAMPLER_PACKAGE_FIXTURE_DIR ${REASAMPLER_TESTS_DIR}/fixtures/package_compat)
 include(${CMAKE_CURRENT_SOURCE_DIR}/cmake/reasampler_targets.cmake)
 
 enable_testing()