Support HTTP Traceparent header field reading in Go 1.24

[grcevski]

Swiss maps have been enabled by default in Go main, which means they will probably become the default in Go 1.24 and break the reading of the HTTP request maps. gRPC is not affected, since we read an array there.

https://go-review.googlesource.com/c/go/+/574516

Go 1.24 is scheduled for release in February (2nd week), we need a fix by then: https://docs.google.com/presentation/d/1jvc0RzrshOOjkeEnsyea2jwjs_zVOcyETG558pqPOK0/mobilepresent?slide=id.g840eaeb4b4_0_0

One possible fix for this is to write a version of the map lookup code which is meant for Swiss maps. Based on some quick code reading I did, this looks more complex now than it used to be.

Another possible solution we discussed at the Go Auto SIG today is potentially reading the Traceparent field while the headers are being parsed, although this will be slower since we will run a uprobe on every header field. The advantage of this approach is that this works for all Go versions.

[grcevski]

I also realized that maybe we simply need to figure out how to work with the swiss maps. To support manual spans we also read a Go map in fill_partial_tracer_id_from_tracers_map, which also reads a Go map.