fix: inject version via -ldflags so releases stop drifting (#1081)

[ChrisJr404]

Closes #1081.

Background

The Amass version string is hard-coded as a const in internal/afmt/print.go:

const (
    Version = "v5.1.1"
    ...
)

This relies on every release remembering to bump the constant by hand. Per @lc's report on #1081, v5.0.1 was tagged with the constant still set to "v5.0.0", so the binary self-identified as v5.0.0 at runtime. That's a release-process bug rather than a code bug, but a tiny code change makes it impossible for it to recur.

Change

1. Convert Version from const to var so the linker can rewrite it. The other afmt constants (Author, Description, DiscordInvitation) stay const since they don't drift between releases.

2. Add an -ldflags injection in .goreleaser.yaml that sets Version to the actual git tag at release time:

   ldflags:
     - -s -w
     - -X github.com/owasp-amass/amass/v5/internal/afmt.Version=v{{ .Version }}

3. Keep the source-level value as the fallback for go install-style builds that don't go through goreleaser.

Verification

$ go build -ldflags "-X github.com/owasp-amass/amass/v5/internal/afmt.Version=v9.9.9-test" -o amass ./cmd/amass
$ ./amass --help 2>&1 | grep "v[0-9]"
                                                                 v9.9.9-test       # ✓ ldflags applied

$ go build -o amass ./cmd/amass
$ ./amass --help 2>&1 | grep "v[0-9]"
                                                                      v5.1.1       # ✓ source fallback

The -s -w flags strip the symbol/debug tables (standard for release binaries — saves ~25% of the binary size for amass) and are conventional alongside -X. Happy to drop them if that's a stylistic preference.

Notes

• Diff is +10 / -3 lines across two files.
• Goreleaser's template variable {{ .Version }} is the tag with the v prefix stripped, so I prepend v in the -X flag — that matches the existing "v5.1.1" style and what users see at runtime today.
• This is independent of the per-release "remember to bump the constant" workflow — that workflow can be retired entirely once this is in (or kept as an extra belt-and-suspenders, since the source fallback won't be wrong if releases are still bumped).