test(parity): add error-case and edge-semantics coverage

[vieiralucas]

Summary

Expands parity from 7 happy-path tests to 15, focused on the drift-prone surfaces that real-AWS comparison actually catches: error codes, conditional writes, filter policies, FIFO ordering, multipart upload, data-key generation.

New tests

Service	Test	What it protects against
SQS	`get_queue_url` on missing queue	Error code drift (`QueueDoesNotExist`)
SQS	FIFO queue with content-based dedup	FIFO ordering + dedup semantics
SNS	Subscription filter policy	Attribute-based filtering actually filters
S3	`get_object` on missing key	Error code drift (`NoSuchKey`)
S3	5 MiB multipart upload	Part-size handling, completion, byte-identical round-trip
DynamoDB	`Query` with `KeyConditionExpression`	Composite-key Query + sort order
DynamoDB	Conditional `PutItem`	`ConditionalCheckFailedException` code on attribute_not_exists
KMS	`GenerateDataKey` + decrypt	32-byte AES key round-trip through Decrypt
SecretsManager	`get_secret_value` on missing secret	Error code drift (`ResourceNotFoundException`)

Local run against fakecloud: 15/15 pass. Weekly real-AWS run will pick them up automatically on the next scheduled or dispatched tick.

Test plan

• `cargo test -p fakecloud-parity` — 15/15 pass against local fakecloud
• `cargo clippy -p fakecloud-parity --tests -- -D warnings` — clean
• `cargo fmt` — clean
• CI `Parity (fakecloud)` job runs green
• Next weekly real-AWS run confirms parity

---

Summary by cubic

Expands the parity test suite from 7 to 15 to lock in real-AWS error codes and edge-case semantics. Covers SQS, SNS, S3, DynamoDB, KMS, and Secrets Manager to reduce drift in high-risk paths.

• New Features
  • Error parity: SQS get_queue_url on missing queue, S3 get_object on missing key, Secrets Manager get_secret_value on missing secret, DynamoDB conditional PutItem failure code.
  • Edge semantics: SQS FIFO ordering with content-based dedup, SNS subscription filter policy, S3 5 MiB multipart upload round-trip, DynamoDB Query on composite key with sort order, KMS GenerateDataKey + Decrypt round-trip.

^{Written for commit 665370a. Summary will update on new commits.}

[cubic-dev-ai]

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