Improve log messages for model_lock

[orichters]

old:

2023-09-29 22:09:37: acquiring model lock...
acquired model lock in 3.9 secs.

new:

2023-09-29 22:09:37: try to acquire model lock...
2023-09-29 22:09:41: acquired model lock in 3.9 secs.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (c395010) 34.90% compared to head (f188569) 34.94%.

❗ Current head f188569 differs from pull request most recent head fdce8bd. Consider uploading reports for the commit fdce8bd to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #76      +/-   ##
==========================================
+ Coverage   34.90%   34.94%   +0.03%     
==========================================
  Files          51       51              
  Lines        1693     1694       +1     
==========================================
+ Hits          591      592       +1     
  Misses       1102     1102              

Files	Coverage Δ
R/model_lock.R	71.42% <100.00%> (+1.42%)	⬆️

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