fix(readers): fail fast on unresolved input paths

[mohammadaaftabv]

Summary

• Fail fast with actionable diagnostics when no supported input files resolve, with allow_empty=True for intentional empty sources.
• Normalize strings, path-like values, directories, globs, local URIs, and chained fsspec paths across worker working directories.
• Prefer construction-anchored inputs, safely fall back to executor working-directory paths, and deduplicate results.

Validation

Focused partitioning, file-utility, and downstream audio/text reader suites pass. Ruff, pre-commit, and DCO checks pass.

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