fix: validate configured language in plain piped output

[ryanchou1994]

When bat -l InvalidSyntax writes to a pipe, it currently copies the input and exits successfully. Forcing colored output reports the unknown language instead. Validate a configured language before creating the simple printer so plain piped output reports the same error, including for empty input. Valid languages still pass the input through unchanged, and output without a configured language keeps lazy syntax loading.

The regression tests cover both error cases, language names and extension tokens, unchanged CRLF/tab output, and a damaged syntax cache that plain output does not need to read. The existing attached-option-value test now uses the valid crontab language, retaining its check that b and n inside a language value do not enable line numbering.

Validation on Linux with Rust 1.98.0:

• The two error regressions fail before the fix and pass after it.
• cargo test --locked --offline -- --test-threads=2: 455 passed, 5 ignored.
• cargo fmt -- --check.
• cargo clippy --locked --offline --all-targets --all-features -- -D warnings.

Refs #2372.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.