feat(gnomod)!: forbid require and find dependencies without it

[n0izn0iz]

A step towards the importer package (#2932) and future of gno.mod (#2904)

• BREAKING CHANGE: remove require statement support from gno.mod
• BREAKING CHANGE: remove -v (verbose) and --remote flags in gno mod download
• Don't require version specification in gno.mod's replace statements
• Use .gno files import statements to find dependencies
• Extract and refacto imports gathering utils in gnovm/pkg/packages
• Add gnovm/cmd/gno/internal/pkgdownload.PackageFetcher interface
• Implement PackageFetcher using vm/qfile queries in gnovm/cmd/gno/internal/pkgdownload/rpcpackagefetcher
• Rewrite single package download routine in gnovm/cmd/gno/internal/pkgdownload
• Move and refacto dependencies download routine in gnovm/cmd/gno/download_deps.go
• Add a --remote-overrides flag for gno mod download that takes chain-domain=rpc-url comma-separated pairs to override endpoints used to fetch packages
• Add and use a testing implementation of PackageFetcher called examplesPackageFetcher that serves package from the examples directory for testing purposes (download tests before this PR use the portal loop public endpoint)
• Make ReadMemPackage and it's dependencies error-out instead of panicking
• Create panicking MemPackage utils that wrap the erroring ones and use them at existing callsites

I decided to do this first to avoid having multiple ways to resolve dependencies lying around in the codebase and causing confusion in subsequent steps

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

[thehowl]

Pre-approving, mostly looks good now. Here's a few further improvements, that I think you can look to tackle in further PRs:

1. Stop swallowing errors: there's a bunch of cases we brought up here, errors will happen in these scenarios and we need to report them properly. I understand you didn't want to include it in the scope of this already large PR, but we need to address it
2. Purify the scope of package gnomod (should be: modules) and move some things to packages, and also change gno mod download -> gno get. Package download is now tied to packages, rather than the requires in the modules; so the command should reflect that. I think gnomod does extra things related to packages, which actually fall outside of its scope.
3. -u flag: we need a way to force an update from the cache, especially now that we still heavily use the portal loop.