chore(docs): fix incorrect usage of 'a' and 'an' across various files

[Pricstas]

This pull request addresses typos in the documentation by correcting the usage of the articles "a" and "an" in several files.

• File: snark-verifier/src/loader/halo2/shim.rs

  • Changed "Assign a elliptic curve point constant" to "Assign an elliptic curve point constant."
  • Changed "Assign a elliptic curve point witness" to "Assign an elliptic curve point witness."

• File: snark-verifier/src/pcs/kzg/accumulator.rs

  • Changed "Instructions to encode/decode a elliptic curve point into/from limbs" to "Instructions to encode/decode an elliptic curve point into/from limbs."

• File: snark-verifier/src/util/transcript.rs

  • Changed "Read a elliptic curve point" to "Read an elliptic curve point."
  • Changed "Write a elliptic curve point" to "Write an elliptic curve point."