feat(go-config): multi-format codecs, envc CLI, fixtures, ASRs

- Module github.com/eslider/go-config with env/yaml/json/ini packages
- internal: source, keymap, merge, structconv, bytesutil
- cmd/envc: convert, get, merge
- docs/asr ASR-0001..0008, README/CHANGELOG/AGENTS refresh
- golangci-lint v2 config; tests + fixtures

Co-authored-by: Cursor <cursoragent@cursor.com>

fixtures/identity/service.ini

@@ -0,0 +1,12 @@
+[service]
+name = my-service
+
+[service.subservice]
+name = abc
+key = abs
+timeout = 30
+enabled = true
+
+[service.database]
+url = postgres://localhost:5432/db
+pool-size = 10