fix(#950): keep line-zero defects with line-specific unlint

[VasilevNStas]

Fixes #950.

Problem

In LtUnlint.defects() the loop that re-adds non-suppressed defects uses the guard line != 0 && defect.line() == line. When a lint produces a defect at line 0 (e.g. mandatory-package reports at line 0 when the whole +package meta is absent) and the EO program also contains a line-specific +unlint mandatory-package:5, the defect at line 0 is silently discarded: global is set, line 0 stays in problematic but is skipped by line != 0, and the fallback if (!added.get() && !global) is also skipped because global is true.

Solution

Drop the line != 0 guard in the re-add loop and compare defect.line() == line only. Line 0 is an intentional production case (lineno.xsl and empty-object.xsl handle it explicitly) and is only meant to be suppressed by a global +unlint lint-name, never by a line-specific +unlint lint-name:N.

Changes

• src/main/java/org/eolang/lints/LtUnlint.java — re-add defects on line 0 when their line stays problematic.
• src/test/resources/org/eolang/lints/unlint-mandatory-package-line.eo — new fixture: no +package, +unlint mandatory-package:5.
• src/test/java/org/eolang/lints/LtUnlintTest.java — new test keepsLineZeroDefectWithLineSpecificUnlint (failed before the fix).

Tests

• LtUnlintTest — 12 tests green (incl. new one).
• Regression LtByXslTest, SourceTest, PkMonoTest, MonoLintsTest, LtUnlintNonExistingDefectTest — 443 tests green after mvn clean.
• mvn -Pqulice install — clean.

[volodya-lombrozo]

Thanks for working on this! Unfortunately the commits aren't GPG/SSH-signed, which rultor needs to merge. GitHub's signing guide: https://docs.github.com/en/authentication/managing-commit-signature-verification/signing-commits. Closing for now — happy to see this reopened once signed.

[VasilevNStas]

@volodya-lombrozo, fixed — commits are now SSH-signed (verified by GitHub). Since the closed PR can't be reopened after a force-push, I've recreated it as #1232 (same change, signed commits).