feat: various improvements on 'gnodev test'

[moul]

• Move testrun.go into test.go because the file is still not too big and right now we've one file per subcommand
• Integreted look and feel both of _filetest and _test?
• Refactor codebase parts where it was not obvious what belongs to a filetest and same for test
• Deduplicate code and make it easier to create testing gno.Machine
• Support Using std.XXX (std.AssertOriginCall(),...) in tests
• Write more unit tests

Continues #208, and this comment (#208 (comment)) by @anarcher

---

Example:

$ go run ./cmd/gnodev test ./examples/gno.land
?       ./examples/gno.land/p/avl       [no test files]
?       ./examples/gno.land/p/bank      [no test files]
?       ./examples/gno.land/p/dom       [no test files]
?       ./examples/gno.land/p/grc/grc20         [no test files]
?       ./examples/gno.land/p/grc/grc20/impl    [no test files]
?       ./examples/gno.land/p/grc/grc721        [no test files]
?       ./examples/gno.land/p/groups    [no test files]
?       ./examples/gno.land/p/maths     [no test files]
ok      ./examples/gno.land/p/rand      2.202855228s
?       ./examples/gno.land/p/releases  [no test files]
?       ./examples/gno.land/p/tests     [no test files]
?       ./examples/gno.land/p/testutils         [no test files]
?       ./examples/gno.land/p/ufmt      [no test files]
?       ./examples/gno.land/r/banktest  [no test files]
?       ./examples/gno.land/r/boards    [no test files]
ok      ./examples/gno.land/r/foo20     3.129722682s
?       ./examples/gno.land/r/nft       [no test files]
ok      ./examples/gno.land/r/releases-example  31.541257ms
?       ./examples/gno.land/r/tests     [no test files]
?       ./examples/gno.land/r/tests_foo         [no test files]
ok      ./examples/gno.land/r/users     37.831148714s
$

$ go run ./cmd/gnodev test ./examples/gno.land/p --verbose 
?       ./examples/gno.land/p/avl       [no test files]
?       ./examples/gno.land/p/bank      [no test files]
?       ./examples/gno.land/p/dom       [no test files]
?       ./examples/gno.land/p/grc/grc20         [no test files]
?       ./examples/gno.land/p/grc/grc20/impl    [no test files]
?       ./examples/gno.land/p/grc/grc721        [no test files]
?       ./examples/gno.land/p/groups    [no test files]
?       ./examples/gno.land/p/maths     [no test files]
=== RUN   TestInstance
--- PASS: TestInstance (667.506µs)
=== RUN   TestIntn
--- PASS: TestIntn (14.12614ms)
=== RUN   file/rand0_filetest.gno
--- PASS: file/rand0_filetest.gno (28.948863ms)
ok      ./examples/gno.land/p/rand      2.173592279s
?       ./examples/gno.land/p/releases  [no test files]
?       ./examples/gno.land/p/tests     [no test files]
?       ./examples/gno.land/p/testutils         [no test files]
?       ./examples/gno.land/p/ufmt      [no test files]
$