tvkit v0.18.0

Refused-request reporting, reported by @xgboosted in #59.

Fixed

• A symbol or interval that TradingView refuses is reported as what it is, not as "Invalid
  interval or bars count". TradingView answers such a request with a symbol_error and/or a
  series_error frame that carries a reason. tvkit skipped the symbol_error and replaced the
  series_error with a fixed message blaming the interval or bars_count, which no retry could
  fix. The exception now carries TradingView's reason verbatim — permission denied (group economics_paid) for ECONOMICS: and FRED: symbols on anonymous sessions, invalid symbol
  for an unknown symbol, unsupported resolution: INDEX:NDFI, 5, seconds_not_entitled,
  custom_resolution — and is raised on the first refusal frame.

• get_ohlcv() and get_quote_data() raise on a refusal instead of ending silently. The
  streams' skip-malformed-frames guard swallowed the error, so a refused symbol produced an empty
  stream (or, for quotes, a short one) and no exception. The documented Raises behaviour now
  holds.

Added

• SeriesError and EntitlementError, exported from tvkit.api.chart.
  SeriesError(ValueError) is raised for every symbol_error / series_error;
  EntitlementError subclasses it for refusals that say the session is not entitled
  (permission denied, *_not_entitled) — permanent, do not retry. Both carry symbol,
  interval, message_type, reason and details. Subclassing ValueError keeps existing
  except ValueError handlers working and keeps tvkit.batch from retrying them; they are
  deliberately not ChartErrors, and not the built-in PermissionError (an OSError, which
  retry policies commonly treat as transient).

Changed

• Messages and types for refused requests. Code matching the text "Invalid interval or bars count" no longer matches. series_error messages keep the "TradingView series error" prefix;
  symbol_error messages start with "TradingView could not resolve symbol". In tvkit.batch,
  ErrorInfo.exception_type for these failures is "SeriesError" or "EntitlementError"
  instead of "ValueError".

• Segmented fetches raise the refusal itself. SegmentedFetchService no longer wraps a
  SeriesError in SegmentedFetchError: TradingView refused the whole request, not one segment,
  so except EntitlementError around get_historical_ohlcv() works whether or not the range was
  segmented. Other segment failures are still wrapped.

• One ERROR log line per refusal — the message and the raw frame — instead of four lines
  blaming the interval and bars_count.