perf(parser): remove the ? operator?

[Boshen]

From Twitter:

• MiniJinja author said avoiding ? improved both the compile time and the runtime performances.
• dtolnay said they don't use ? operators in serde and serde-json "because it is too slow".
• serde has their own try! macro that avoids type conversion https://github.com/rust-lang/rust/issues/37939
• mitsuhiko says its still not fix

[Boshen]

The conclusion seems to be ? still affects compile times, but not runtime.