attachments: validate file encryption inputs

[Ap4sh]

summary

the file-based attachment encryption overloads currently read 32 bytes from seed without checking its size, unlike the buffer overloads. they also ignore allow_large, so files above MAX_REGULAR_SIZE are accepted when the flag is false

this validates both inputs before hashing the file while keeping oversized file support when allow_large=true

tests

• ./Build/tests/testAll "Attachment file encryption validates its inputs"
• ./Build/tests/testAll "[attachments]"
• ./Build/tests/testAll
• ./utils/ci/drone-format-verify.sh

[jagerman]

I've also chased down the equivalent code (which is vastly rewritten) in the pfs branch, and these exceptions match what is raised there.