Add support for fluid simulation caches

Add `eModifierType_Fluid` support, with non-pointcache caches. The entire
cache directory is considered a dependency to list/pack.

CHANGELOG.md

@@ -3,6 +3,10 @@
 This file logs the changes that are actually interesting to users (new features,
 changed functionality, fixed bugs).
 
+# Version 1.15 (in development)
+
+- Add support for fluid simulation caches.
+
 # Version 1.14 (2022-09-12)
 
 - While tracing dependencies, call the progress callback function before opening a blend file, instead of before iterating over its contents. The opening (and loading of SDNA) takes a significant amount of time, so this will make any UI (like the Flamenco add-on) report the right filename when waiting for big files.

blender_asset_tracer/cdefs.py

@@ -48,6 +48,7 @@ eModifierType_WeightVGProximity = 38
 eModifierType_Ocean = 39
 eModifierType_MeshCache = 46
 eModifierType_MeshSequenceCache = 52
+eModifierType_Fluid = 56
 eModifierType_Nodes = 57
 
 # DNA_particle_types.h

blender_asset_tracer/trace/modifier_walkers.py

@@ -278,6 +278,34 @@ def modifier_smoke_sim(
     )
 
 
+@mod_handler(cdefs.eModifierType_Fluid)
+def modifier_fluid(
+    ctx: ModifierContext, modifier: blendfile.BlendFileBlock, block_name: bytes
+) -> typing.Iterator[result.BlockUsage]:
+    my_log = log.getChild("modifier_fluid")
+
+    domain = modifier.get_pointer(b"domain")
+    if domain is None:
+        my_log.debug(
+            "Modifier %r (%r) has no domain", modifier[b"modifier", b"name"], block_name
+        )
+        return
+
+    # See fluid_bake_startjob() in physics_fluid.c
+    path = domain[b"cache_directory"]
+    path, field = domain.get(b"cache_directory", return_field=True)
+
+    log.info("   fluid cache at %s", path)
+    bpath = bpathlib.BlendPath(path)
+    yield result.BlockUsage(
+        domain,
+        bpath,
+        path_full_field=field,
+        is_sequence=True,
+        block_name=block_name,
+    )
+
+
 @mod_handler(cdefs.eModifierType_Cloth)
 def modifier_cloth(
     ctx: ModifierContext, modifier: blendfile.BlendFileBlock, block_name: bytes