Add time columns to output and make some code improvements

[SaiedKazemi]

This commit adds probe transmit and reply receive times to the output it generates. This commit also makes some code improvements.

The changes were tested locally using .jsonl archives from GCS.

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 495

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.86%

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Totals
Change from base Build 491:	0.0%
Covered Lines:	617
Relevant Lines:	637

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💛 - Coveralls

[SaiedKazemi]

@stephen-soltesz Thank you for your review. I've made edits based on your and Maxime's feedback. PTAL.

[SaiedKazemi]

cmd/trex/main.go line 213 at r1 (raw file):

Previously, stephen-soltesz (Stephen Soltesz) wrote…

Did you also consider `fmt.Fprintf` and `bytes.Buffer` for this case?

I left it as is for now unless you think it's important to change it.

[SaiedKazemi]

PTAL.