fix: Validate metadata len in IPC reader

[JakeDern]

Which issue does this PR close?

No issue filed.

Rationale for this change

We allocate memory based on metadata length - If an untrusted client writes a meta len of < 0 then we'll allocate a large number of bytes due to sign extension and likely panic.

What changes are included in this PR?

• Update StreamReader in both places it reads metadata length for < 0 which is at the start of the stream to read the schema, and in the middle of the stream between each message.

Are these changes tested?

Yes, tests for both reads are added

Are there any user-facing changes?

No

[alamb]

Thanks @JakeDern -- I have a style comment but I think it is stylistic rather than substantitive

cc @viirya and @tustvold for your thoughts

[viirya]

Why do we need this? I thought that you already include the fix in #8001.

[JakeDern]

@viirya Andrew requested I make a separate fix - The other PR may not make it until the next major release in October as it could have an API change.