Tezt: let transfer terminate in transfer_and_wait_for_injection

Context

Related to #1529

The Tezt test Alpha: Test monitor_operations RPC occasionally leaves processes hanging, which are eventually terminated by tezt. However, when run under bisect instrumentation, this termination occasionally corrupts the written coverage data.

Manually testing the MR

This error can be reproduced by running the following script reproduce-bisect-error.sh:

#!/bin/sh

set -e

make coverage-clean
BISECT_FILE=$(pwd)/_coverage_output/ dune exec tezt/tests/main.exe -- $@ -t "Alpha: Test monitor_operations RPC"
make coverage-report-summary

To run it, first make octez with instrumentation and then loop the script:

COVERAGE_OPTIONS="--instrument-with bisect_ppx" BISECT_FILE=$(pwd)/_coverage_output/ make
while ./reproduce-bisect-error.sh; do done

within short, you should see:

[12:51:50.985] [SUCCESS] (1/1) Alpha: Test monitor_operations RPC
bisect-ppx-report: internal error, uncaught exception:
                   Bisect_common.Invalid_file("_coverage_output/173366172.coverage", "unexpected end of file while reading magic number")
                   
make: *** [Makefile:112: coverage-report-summary] Error 125

this MR fixes the issue by updating transfer_and_wait_for_injection so that:

• the call to client initiating a transfer does not wait for confirmation
• it waits for the call to the client to terminate
• and then it waits for the injection

After which, running:

while ./reproduce-bisect-error.sh; do done

no longer reports any errors.

I'm not sure about the lwt/tezt event stuff in this MR. Wait happens if the injection has already happened when the wait_for promise is scheduled?

Checklist

• n/a Document the interface of any function added or modified (see the coding guidelines)
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• n/a Provide automatic testing (see the testing guide).
• n/a For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, the Development Version section of CHANGES.md for everything else).
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