store: support nested file groups with custom ordering

[dirkdev98]

Closes #319

[github-actions]

==== Benchmark result ====

Total benchmarks: 9
          Passed: 9
          Failed: 0
-----------
object validator simple      2000000  iterations     509  ns/op
object validator nested        50000  iterations   48310  ns/op
logger - strings              500000  iterations    3599  ns/op
logger - objects              500000  iterations    3677  ns/op
logger - deep objects         200000  iterations    5005  ns/op
uuid                         2000000  iterations     525  ns/op
uuid.isValid                10000000  iterations     157  ns/op
isNil                      500000000  iterations       0  ns/op
isPlainObject              100000000  iterations      18  ns/op

[github-actions]

==== C8 test coverage ====
Statements: 72.68% ( 17050/23458 )
Branches : 71.62% ( 2016 /2815 )
Functions : 71.96% ( 634 /881 )
Lines : 72.68% ( 17050 /23458 )