fix: derive Go import identifiers from the package, not the path segment

[dudell-bud]

Problem

The unused-import detector uses the last path segment of an import path as the in-code identifier. In Go that is frequently wrong, so every affected import gets reported as unused.

Scanning a real Go repo (desloppify --lang go scan) produced 20 false positives and no true positives:

Import	Reported	Actually used as
_ "github.com/joho/godotenv/autoload"	unused import: autoload	nothing — blank import, for init() side effects
"gopkg.in/yaml.v3"	unused import: v3	yaml.Unmarshal(...)
"math/rand/v2"	unused import: v2	rand.N(...)
"github.com/go-playground/validator/v10"	unused import: v10	validator.New()
"github.com/anthropics/anthropic-sdk-go"	unused import: anthropic-sdk-go	anthropic.MessageParam

Note the last row can never be right: - is not legal in a Go identifier.

There is also a general argument for treating this class conservatively: go build fails on a genuinely unused import, so a Go module that compiles cannot have one. Any finding of this class on a compiling module is therefore a false positive.

Fix

Go now gets its own identifier resolver instead of the generic path-segment heuristic:

• Blank (_) and dot (.) imports are skipped. A blank import exists purely for its init() side effect and is never "used" by design; a dot import injects every exported name with no qualifier to search for.
• Major-version segments are stripped — /v2, /v10, and gopkg.in-style yaml.v3.
• Unresolvable names return None, and callers treat None as "do not report". Where the package clause cannot be determined from the path alone (e.g. a hyphenated repo name), staying silent is the right call: a false negative costs far less than a false positive.

Verification

• python -m pytest desloppify/tests/ -q → 5825 passed, 3 skipped
• Added desloppify/tests/lang/common/test_go_unused_imports.py covering each case in the table above.
• Scanned the repo that surfaced this: its 17 unused-import findings drop to 0, with no new findings elsewhere.

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