Preserve orphan comments (e.g. kubebuilder scaffold marker) inside import blocks

[devthedevil]

Summary

Fixes #135. Since PR #120 ("optimize detect import blocks"), gci silently drops any comment inside an import block that isn't attached (as Doc or trailing Comment) to a specific *ast.ImportSpec. That PR's own description acknowledged this as a known breaking change ("introduce breaking change: remove isolated comments").

The most common way to hit this is a standalone marker comment such as:

import (
	"os"
	"fmt"
	// +kubebuilder:scaffold:imports
)

kubebuilder/controller-gen relies on that comment being present at that exact position to know where to insert future imports. Running gci on such a file removes the marker entirely, which breaks the codegen workflow.

Root cause

pkg/parse/parse.go's ParseFile only records byte ranges for import specs (Start/End derived from each spec's Doc/Name/Path/Comment). pkg/gci/gci.go's LoadFormat rebuilds the import block purely by concatenating those recorded byte ranges, so any comment that isn't formally attached to a spec never makes it into the rewritten output.

Change

• pkg/parse/parse.go: added findTailComment, which scans f.Comments for a comment group that sits after the last recognized import spec but before the import block's closing paren (i.e. not attached to any spec). ParseFile now additionally returns that comment's byte range (-1, -1 if none exists).
• pkg/gci/gci.go: LoadFormat takes the two new return values and, right before appending the closing ), re-inserts the orphan comment's original bytes so it survives the rewrite.
• pkg/gci/testdata.go: added a trailing-marker-comment test case reproducing the exact example from the issue.

The change is intentionally scoped to the trailing-comment case described in the issue (a comment between the last import and the closing paren). A related but distinct case mentioned in the issue discussion — a leading orphan comment ending up merged onto the import ( line — is not addressed here to keep this change minimal and focused.

Testing

Added trailing-marker-comment to pkg/gci/testdata.go's testCases, which is exercised by the existing TestRun in pkg/gci/gci_test.go:

in: `package main

import (
	"os"
	"fmt"
	// +kubebuilder:scaffold:imports
)
`,
out: `package main

import (
	"fmt"
	"os"
	// +kubebuilder:scaffold:imports
)
`,

I don't have a Go toolchain available in the environment I drafted this in, so I hand-traced the AST byte offsets against this reproduction case and against the existing fixtures (multi-block imports, comments outside the import block, cgo blocks, etc.) to check for regressions, but please run CI/go test ./... before merging.

Closes #135