fix: reject malformed --go-version values

[AtiqDev (atiqur-rahman-pro)]

• Replace loose regex matching with strictGoVersionPattern anchored to input boundaries
• Reject invalid version strings like '1.24x', 'invalid.ver', and 'abc1.24'
• Add TestNormalizeGoVersionStrictRejection regression tests

---

Summary

This PR makes validation of the explicit --go-version argument stricter.

Currently, a malformed value containing trailing characters is accepted because the parser extracts a valid-looking version
substring instead of validating the complete input.

Reproduction

Environment:

• Windows amd64
• Go 1.26.7
• Upstream commit reviewed: 40781f167719913666fe2a7dc1c77ea6f256df0a

go run . list --go-version=1.24invalid
echo %ERRORLEVEL%

Current behavior
The value is interpreted as Go 1.24.
Go 1.24 guidelines are printed.
The command exits with code 0.

Documented valid formats should continue to work:

1.24
go1.24.3
devel
Changes
Validate the complete explicit Go-version value instead of accepting a matching substring.
Add regression coverage for trailing invalid characters.
Preserve support for valid version formats and Go toolchain output.
Verification
cmd

go test -count=1 ./...
go vet ./...
gofmt -l .
Manual negative case:

cmd

go run . list --go-version=1.24invalid
echo %ERRORLEVEL%
Expected: parsing error and nonzero exit code.

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corrected version:

## Summary

This PR makes validation of the explicit `--go-version` argument stricter.

Currently, a malformed value containing trailing characters is accepted because the parser extracts a valid-looking version
substring instead of validating the complete input.

## Reproduction

Environment:

- Windows amd64
- Go 1.26.7
- Upstream commit reviewed: `40781f167719913666fe2a7dc1c77ea6f256df0a`

```cmd
go run . list --go-version=1.24invalid
echo %ERRORLEVEL%

## Current behavior

- The value is interpreted as Go 1.24.
- Go 1.24 guidelines are printed.
- The command exits with code 0.

## Expected behavior

The CLI should reject 1.24invalid as malformed and return a nonzero exit code.

Documented valid formats should continue to work:

- 1.24
- go1.24.3
- devel

## Changes

- Validate the complete explicit Go-version value instead of accepting a matching substring.
- Add regression coverage for trailing invalid characters.
- Preserve support for valid version formats and Go toolchain output.

## Verification

go test -count=1 ./...
go vet ./...
gofmt -l .

Manual negative case:

go run . list --go-version=1.24invalid
echo %ERRORLEVEL%

Expected result: a parsing error and a nonzero exit code.

## Note

Issue creation is restricted in this repository, so I am submitting this focused PR directly for maintainer review.

Use the **Changes** section only if your branch already contains those code and test changes.