Split up archive.go into type-specific files; add wider zlib support

[egibs]

This PR splits up all of the archive-specific functions in archive.go into their own respective files for readability.

As part of this, I also added extension-agnostic zlib support depending on whether the file returns &{.Z, application/zlib} from programkind.File.

I also fixed a panic:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xd648e6]

goroutine 19400 [running]:
github.com/chainguard-dev/malcontent/pkg/action.extractGzip({0x2b5ce48?, 0xc0000ff6b0?}, {0xc001d680c0, 0x39}, {0xc0009b8240, 0x85})
	github.com/chainguard-dev/[email protected]/pkg/action/archive.go:249 +0x2c6
github.com/chainguard-dev/malcontent/pkg/action.extractArchiveToTempDir({0x2b5ce48, 0xc0000ff6b0}, {0xc0009b8240, 0x85})
	github.com/chainguard-dev/[email protected]/pkg/action/archive.go:653 +0x383
github.com/chainguard-dev/malcontent/pkg/action.processArchive({0x2b5ce48, 0xc0000ff6b0}, {0x8, 0x0, 0x0, 0x0, 0x0, 0x1, {0x0, 0x0, ...}, ...}, ...)
	github.com/chainguard-dev/[email protected]/pkg/action/scan.go:496 +0x134
github.com/chainguard-dev/malcontent/pkg/action.recursiveScan.func1({0xc0009b8240, 0x85})
	github.com/chainguard-dev/[email protected]/pkg/action/scan.go:328 +0xd0
github.com/chainguard-dev/malcontent/pkg/action.recursiveScan.func4()
	github.com/chainguard-dev/[email protected]/pkg/action/scan.go:436 +0xa2
golang.org/x/sync/errgroup.(*Group).Go.func1()
	golang.org/x/[email protected]/errgroup/errgroup.go:78 +0x50
created by golang.org/x/sync/errgroup.(*Group).Go in goroutine 19398
	golang.org/x/[email protected]/errgroup/errgroup.go:75 +0x96

This was happening because we were trying to print ft.Ext debug logs for files that returned nil from programkind.File.

[egibs]

These lines, L101-112, L152-162, and the additions in zlib.go are the only material changes in this PR. The rest are just moving existing code into new files (and updating the debug logging in gzip.go.

[tstromberg]

It looks good; what do you think about moving this out of action and into an archive package? It feels like archive handling has grown up into its own feature at this point.

[egibs]

It looks good; what do you think about moving this out of action and into an archive package? It feels like archive handling has grown up into its own feature at this point.

I ran into some circular imports earlier but I can give it a try.

[egibs]

It looks good; what do you think about moving this out of action and into an archive package? It feels like archive handling has grown up into its own feature at this point.

Updated in 43b922d (#723).

I left archive_test.go in action since it uses Scan and CachedRules. I also moved the extension and archive map code to programkind since that seemed like a better fit.