replace fs access with afero

[nofun97]

This PR replaces os.File and ioutil.ReadFile with afero to avoid direct os access.

Checklist:

• [ ] Added related tests
• [ ] Made corresponding changes to the documentation

[coveralls]

Pull Request Test Coverage Report for Build 1c4d90f6e34ae09ca88a1bfea37dbd5794f777fa-PR-610

• 24 of 37 (64.86%) changed or added relevant lines in 5 files are covered.
• 9 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.04%) to 48.483%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
cmd/arrai/run.go	3	4	75.0%
cmd/arrai/test.go	2	3	66.67%
cmd/arrai/sync_other.go	0	4	0.0%
syntax/std_os_nonwasm.go	15	22	68.18%
<!--	Total:	24	37	64.86%	-->

Files with Coverage Reduction	New Missed Lines	%
rel/value_set_str.go	9	55.67%
<!--	Total:	9		-->

Totals
Change from base Build 786abc0179097834e20537f0ba0d71e2805c29a3:	-0.04%
Covered Lines:	4795
Relevant Lines:	9890

---

💛 - Coveralls