fix(size): create new message if size changes

[stephen-soltesz]

Previously, the server would report that the applicationBytesSent was identically the amount requested by the bytes limit parameter. However, the client would see more bytes than expected. This was due to the message size being calculated correctly but a new message not being created.

Since ScaleMessage is called unconditionally, this change now ensures that a new message is created whenever the scaled size is different than the current messageSize.

Now the server application data and the client visible application data should differ only by the size of the final measurement message.

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 7467609891

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.3%) to 69.84%

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Totals
Change from base Build 7453335104:	-0.3%
Covered Lines:	873
Relevant Lines:	1250

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💛 - Coveralls

[stephen-soltesz]

Evidently, internal/latency1/latency1_test.go has a flaky test:

--- FAIL: TestHandler_Result (0.00s)

testing.go:1206: TempDir RemoveAll cleanup: unlinkat /tmp/TestHandler_Result4078838136: directory not empty

I've seen these before but this one seemed to be persistent this time. I'm imagining that the ttlcache is writing to the temp directory after the function returns but before the directory is fully removed. I've added a short delay at the end of the test to work around it. The change includes a TODO to add handler shutdown for a proper fix.

Reviewable status: 0 of 1 approvals obtained (waiting on @robertodauria)

[robertodauria]

Reviewed 1 of 1 files at r2, 1 of 1 files at r3, 1 of 1 files at r4.
Reviewable status: complete! 1 of 1 approvals obtained