ci: enable err113, gosec, godot, perfsprint, lll linters

[creed-bratton]

Enables 5 linters from the planned phase 2 rollout (quick wins, < 30 lines changed).

err113: define a package-level sentinel for the static "missing URL scheme" message; change %v to %w where an underlying error is wrapped; add //nolint:err113 for messages that carry dynamic context (URL, size, HTTP status) and have no underlying error to wrap.

gosec: G404 (math/rand used to pick from a pre-configured auth list, not security-sensitive); G703 (path traversal false positives on file:// URLs already validated by the parser).

godot: add trailing periods to three doc comments in parser.go, v0.go, v1.go, and validations.go.

perfsprint: replace two fmt.Sprintf("%s: ", key) with string concatenation in errors.go.

lll: add a config-level exclusion rule for struct field tag lines (covers all long lines in v0.go/v1.go); split long ValidationWarning literals in fields.go across multiple lines; add //nolint:lll for lines containing long URLs or a regex literal that cannot be shortened without losing meaning; split CLI flag help strings in publiccode-parser/ using string concatenation.

[bfabio]

Please fix the linting errors