feat: use tl::unexpected in Index default implementations

Replace throw std::runtime_error with return tl::unexpected in virtual
method default implementations that return tl::expected<T, Error>.

- 38 methods: return tl::unexpected(Error(ErrorType::UNSUPPORTED_INDEX_OPERATION))
- 8 methods with non-expected return types: keep throw (GetIndexType, GetNumberRemoved, etc)
- CheckFeature: return false instead of throw

Signed-off-by: LHT129 <tianlan.lht@antgroup.com>
Assisted-by: OpenCode:mini-max-M2.7

Author: LHT129