feat(repl): add imports, funcs, commands, etc

[moul]

Still buggy, but better:

$ go run ./gnovm/cmd/gno repl --verbose --imports gno.land/p/demo/ufmt --skip-usage
gno:1> println(42, 43)
42 43
gno:2> println(ufmt.Sprintf("hello %d", 1337))
hello 1337
gno:3> /import gno.land/r/demo/art/millipede
gno:4> println(millipede.Draw(10))   
    ╚⊙ ⊙╝
  ╚═(███)═╝
 ╚═(███)═╝
╚═(███)═╝
 ╚═(███)═╝
  ╚═(███)═╝
   ╚═(███)═╝
    ╚═(███)═╝
    ╚═(███)═╝
   ╚═(███)═╝
  ╚═(███)═╝

gno:5> /src
package test
import "gno.land/p/demo/ufmt"
import "gno.land/r/demo/art/millipede"

func repl_5() {
println(millipede.Draw(10))
}
gno:6> ⏎

ps: I don't like my code, but I prefer adding more features before trying to find the best code architecture for the repl.

Contributors Checklist

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests

Maintainers Checklist

• Checked that the author followed the guidelines in CONTRIBUTING.md
• Checked the conventional-commit (especially PR title and verb, presence of BREAKING CHANGE: in the body)
• Ensured that this PR is not a significant change or confirmed that the review/consideration process was appropriate for the change