perf: batch entry decryption into a single agent round trip

[Chr1s70ph]

Finding an entry by name decrypts every entry in the vault (name, username, folder, notes, uris, custom fields), and each decryption was a separate request to the agent over a fresh socket connection. With a few hundred sequential round trips this took over a second on macos, where per-connection overhead is much higher than on linux.

Add a DecryptMany action to the agent protocol that decrypts a batch of cipherstrings in one round trip, and drive the existing per-entry decryption functions through a record/replay decryptor: a recording pass collects every cipherstring they want (their control flow only depends on the entry structure, never on decrypted values), and after one batched request a replay pass hands the results back out in the same order. rbw get, search, and list all use the batch path now; master password reprompt semantics are unchanged since the agent runs the same per-item handler inside the batch.

Commit was made in assistance with AI

Improves the performance Issues mentioned in #11

before:

/opt/homebrew/bin/rbw get "<secret>" --full  0,12s user 1,69s system 97% cpu 1,848 total

after:

rbw get "<secret>" --full  0,01s user 0,01s system 59% cpu 0,038 total