rust: add len method to SbpMessage

[notoriaga]

While updating the console realized that it was using the sbp_sizemethod (now called encoded_len). This adds a len method to SbpMessage (WireFormat isn't usable by downstream crates). This function is actually a little different, it adds on the 8 bytes for the header + crc, which sbp_size did not. I think this is probably what we actually want in the console, in order to show how much data the console has read

[john-michaelburke]

Finally an explanation for the discrepancy in data rate between new and old console 😄

[silverjam]

Actually I think our nomenclature could use some consideration here. I think usually "encoded len" is used to indicate how big the byte buffer would be if the message was encoded into it's "on wire" representation.

[silverjam]

Actually I think our nomenclature could use some consideration here. I think usually "encoded len" is used to indicate how big the byte buffer would be if the message was encoded into it's "on wire" representation.

See:

• https://developer.apple.com/documentation/metal/mtlargumentencoder/2915784-encodedlength
• https://guava.dev/releases/18.0/api/docs/com/google/common/base/Utf8.html

So maybe we should switch around len and encoded_len or rename len to wire_len or packed_len

[notoriaga]

Great idea, did the switcheroo