feat(#553): add test-word lint

[VasilevNStas]

Fixes #553.

Problem

Objects with names containing the word test (case-insensitive) are allowed, while the project convention requires test names to be clean. Such names should lead to lint warnings.

Solution / What

New XSLT lint test-word that warns when an object name contains test in a test context: object names inside test objects (matched by the eo:test-name() helper), their ancestors, or when the top-level object name ends with -tests.

Changes

• src/main/resources/org/eolang/lints/tests/test-word.xsl — the new lint.
• src/main/resources/org/eolang/motives/tests/test-word.md — motivation.
• src/test/resources/org/eolang/lints/packs/single/test-word/ — 5 test packs.

Tests

• catches-test-in-test-object
• catches-test-word-in-helper
• catches-test-in-nested-object
• allows-clean-test-names
• allows-test-word-in-regular-object

[VasilevNStas]

@volodya-lombrozo please review, I`m fixed it