fix(logging): do not panic in library code

[freelerobot]

fixes: #1862

Changes:

• No longer panic on User introduced errors. Instead we log the error and let program proceed
• We log.Fatalf("ptypes.TimestampProto(time.Unix(0,0)) failed: %v", err) to exit program, since it's a fatal error/likely not induced by Users

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[freelerobot]

After careful consideration:

1. When r.Request is nil, we pipe error message to errc like @tbpg suggested!

2. When protoStruct contains non-parseable but VALID JSON, we don't log to user at all because i) they will already know a property didn't parse correctly (see a nil value) ii) It's not a user error and there's nothing the user can do to solve this issue. So we don't log per client library convention to be less verbose.

"libraries shouldn't log" :)

[freelerobot]

@codyoss ready for your review on previous change requested, thanks!

[codyoss]

LGTM