feat(#1100): add broad-scope lint

[VasilevNStas]

Fixes #1100.

Problem

A private attribute (local) may have an excessively broad scope: it is used only inside a single nested object, while it is declared at a much higher level. This should lead to a lint warning.

Solution / What

New XSLT lint broad-scope modeled after redundant-object: it finds private attributes referenced (via ^ξ(?:\.ρ)*\. base prefixes) exclusively within a single object different from the declaration site, and warns that the scope is too broad.

Changes

• src/main/resources/org/eolang/lints/design/broad-scope.xsl — the new lint.
• src/main/resources/org/eolang/motives/design/broad-scope.md — motivation.
• src/test/resources/org/eolang/lints/packs/single/broad-scope/ — 3 test packs.

Tests

• catches-broad-scope
• allows-used-on-top-level
• allows-used-in-multiple-objects

[VasilevNStas]

@yegor256 @volodya-lombrozo plz review