chore: add codecov config

codecov.yml

@@ -0,0 +1,39 @@
+codecov:
+  require_ci_to_pass: true
+
+coverage:
+  precision: 2
+  round: down
+  range: '70...100'
+
+  status:
+    patch:
+      default:
+        # basic
+        target: auto
+        threshold: 100% # don't require patch to have coverage per se
+        base: auto
+
+    project:
+      default:
+        # basic
+        target: auto
+        threshold: 5%
+        base: auto
+        flags:
+          - unit
+        paths:
+          - 'src'
+
+parsers:
+  gcov:
+    branch_detection:
+      conditional: yes
+      loop: yes
+      method: no
+      macro: no
+
+comment:
+  layout: 'reach,diff,flags,files,tree'
+  behavior: default
+  require_changes: false