[enhancement] Print the performance reference tuple while running only if defined

[jack-morrison]

Prior to change

A test without reference values prints (r:0, l:None, u:None) for each performance variable. This is #3175.

user@myhost:~/reframe-examples/tutorial$ reframe -c stream/stream_runonly.py -r
<snip>

[----------] start processing checks
[ RUN      ] stream_test /2e15a047 @generic:default+builtin
[       OK ] (1/1) stream_test /2e15a047 @generic:default+builtin
P: copy_bw: 136250.6 MB/s (r:0, l:None, u:None)
P: triad_bw: 127052.0 MB/s (r:0, l:None, u:None)
[----------] all spawned checks have finished

[  PASSED  ] Ran 1/1 test case(s) from 1 check(s) (0 failure(s), 0 expected failure(s), 0 skipped, 0 aborted)
[==========] Finished on Mon Jul 14 19:19:13 2025+0000
Log file(s) saved in '/tmp/rfm-wkcpor0o.log'

After change

A test without reference values does not print the reference tuple. Only the captured performance metric is printed.

user@myhost:~/reframe-examples/tutorial$ reframe -c stream/stream_runonly.py -r
<snip>

[----------] start processing checks
[ RUN      ] stream_test /2e15a047 @generic:default+builtin
[       OK ] (1/1) stream_test /2e15a047 @generic:default+builtin
P: copy_bw: 124658.9 MB/s
P: triad_bw: 99002.0 MB/s
[----------] all spawned checks have finished

[  PASSED  ] Ran 1/1 test case(s) from 1 check(s) (0 failure(s), 0 expected failure(s), 0 skipped, 0 aborted)
[==========] Finished on Mon Jul 14 19:13:53 2025+0000
Log file(s) saved in '/tmp/rfm-_jygclgm.log'

A test with reference values behaves as before. The captured performance metric and its references are both printed.

user@myhost:~/reframe-examples/tutorial$ reframe -c stream/stream_runonly.py -r
<snip>

[----------] start processing checks
[ RUN      ] stream_test /2e15a047 @generic:default+builtin
[       OK ] (1/1) stream_test /2e15a047 @generic:default+builtin
P: copy_bw: 133880.3 MB/s (r:137659, l:-0.1, u:0.3)
P: triad_bw: 129926.7 MB/s (r:137659, l:-0.55, u:0.5)
[----------] all spawned checks have finished

[  PASSED  ] Ran 1/1 test case(s) from 1 check(s) (0 failure(s), 0 expected failure(s), 0 skipped, 0 aborted)
[==========] Finished on Mon Jul 14 19:14:31 2025+0000
Log file(s) saved in '/tmp/rfm-2md5inu3.log'

Closes #3175

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.26%. Comparing base (d711e28) to head (b34fab8).
⚠️ Report is 3 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3517   +/-   ##
========================================
  Coverage    91.26%   91.26%           
========================================
  Files           62       62           
  Lines        13581    13583    +2     
========================================
+ Hits         12395    12397    +2     
  Misses        1186     1186           

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