Add pluginPaths support for plugin resolution and resilient plugin loading

[dbale-arg]

Motivation

• Allow Solhint to resolve plugins from additional locations (editor integrations, external projects) instead of depending solely on the current working directory.
• Preserve existing npm-installed plugin behavior while enabling explicit resolution from user-provided pluginPaths in .solhint.json.

Description

• Added pluginPaths support to lib/rules/index.js, normalizing pluginPaths as either a string or an array and building resolution paths including process.cwd(), each configured pluginPath, and each <pluginPath>/node_modules.
• Switched plugin loading to use require.resolve(packageName, { paths }) followed by require(...) so Node resolution searches the configured locations without global hacks.
• Made plugin load failures non-fatal by emitting a warning and returning an empty plugin list so core rules and other plugins still run; also support ESM-style default export as well as direct array exports.
• Updated config schema in lib/config/config-schema.js to accept pluginPaths as string | string[] and added/updated tests in test/common/plugin-loading.js and test/common/config-validator.js to cover the requested cases.

Testing

• Ran the focused tests with npm test -- test/common/plugin-loading.js test/common/config-validator.js and all tests passed.
• Ran lint checks with npx eslint lib/rules/index.js lib/config/config-schema.js test/common/plugin-loading.js test/common/config-validator.js and there were no lint errors after formatting fixes.

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Codex Task