[Typo] "Exected code", "flexiblity" and "heterogenous"

[euprunin]

• "Exected code" ⟶ "Expected code"
• "For the sake of flexiblity" ⟶ "For the sake of flexibility"
• "These heterogenous operators are overloaded" ⟶ "These heterogeneous operators are overloaded"