Fix grammatical errors and improve documentation clarity

[donatik27]

1. denial-of-service.md:

   • Added missing article "an" before "attacker".
   • Corrected "computation" to "computations" for consistency.

2. deprecated.md:

   • Improved sentence structure for better readability.

3. timestamp-dependence.md:

   • Added "the" before "Timestamp Dependence" for consistency.

4. functions-and-events.md:

   • Added "a" before "constructor" for grammatical accuracy.
   • Changed code block language from "sol" to "solidity" for better syntax highlighting.