internal/pkg: content-based dependency substitution

This change introduces a new fast path for FloodArtifact. It is taken when a curing artifact has identical-by-content controlled relevant inputs and are otherwise identical to an already-cured artifact.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/net_test.go

@@ -90,6 +90,7 @@ func TestHTTPGet(t *testing.T) {
 			".":          {Mode: fs.ModeDir | 0700},
 			"checksum":   {Mode: fs.ModeDir | 0700},
 			"identifier": {Mode: fs.ModeDir | 0700},
+			"substitute": {Mode: fs.ModeDir | 0700},
 			"work":       {Mode: fs.ModeDir | 0700},
 		}},
 
@@ -159,6 +160,8 @@ func TestHTTPGet(t *testing.T) {
 			"identifier": {Mode: fs.ModeDir | 0700},
 			"identifier/oM-2pUlk-mOxK1t3aMWZer69UdOQlAXiAgMrpZ1476VoOqpYVP1aGFS9_HYy-D8_": {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/fLYGIMHgN1louE-JzITJZJo2SDniPu-IHBXubtvQWFO-hXnDVKNuscV7-zlyr5fU")},
 
+			"substitute": {Mode: fs.ModeDir | 0700},
+
 			"work": {Mode: fs.ModeDir | 0700},
 		}},
 	})