fix: prevent test.db from being created during unit tests (#3042)

This PR updates the unit tests to use in-memory SQLite databases
(:memory:) instead of creating physical test.db files on disk.

While using tmp directory for managing the test.db file is a plausible
approach, it will encounter file-locking conflicts on Windows during
test cleanup which prevents the clean-up of database files located in
tmp directory.

---------

Co-authored-by: Yuan Teoh <45984206+Yuan325@users.noreply.github.com>

Author: helloeve

cmd/internal/invoke/command_test.go

@@ -52,7 +52,7 @@ func TestInvokeTool(t *testing.T) {
 sources:
   my-sqlite:
     kind: sqlite
-    database: test.db
+    database: ":memory:"
 tools:
   hello-sqlite:
     kind: sqlite-sql

cmd/internal/skills/command_test.go

@@ -59,7 +59,7 @@ func TestGenerateSkill(t *testing.T) {
 sources:
   my-sqlite:
     kind: sqlite
-    database: test.db
+    database: ":memory:"
 tools:
   hello-sqlite:
     kind: sqlite-sql
@@ -158,7 +158,7 @@ func TestGenerateSkill_Toolsets(t *testing.T) {
 sources:
   my-sqlite:
     kind: sqlite
-    database: test.db
+    database: ":memory:"
 tools:
   hello-sqlite:
     kind: sqlite-sql
@@ -247,7 +247,7 @@ func TestGenerateSkill_SpecificToolset(t *testing.T) {
 sources:
   my-sqlite:
     kind: sqlite
-    database: test.db
+    database: ":memory:"
 tools:
   hello-sqlite:
     kind: sqlite-sql

cmd/root_test.go

@@ -699,7 +699,7 @@ func TestFileLoadingErrors(t *testing.T) {
 }
 
 func TestPrebuiltAndCustomTools(t *testing.T) {
-	t.Setenv("SQLITE_DATABASE", "test.db")
+	t.Setenv("SQLITE_DATABASE", "\":memory:\"")
 	// Setup custom config
 	customContent := `
 kind: tool
@@ -867,7 +867,7 @@ tools:
 }
 
 func TestDefaultConfigBehavior(t *testing.T) {
-	t.Setenv("SQLITE_DATABASE", "test.db")
+	t.Setenv("SQLITE_DATABASE", "\":memory:\"")
 	testCases := []struct {
 		desc      string
 		args      []string