Add toString for EtsClassImpl

[Lipen]

This PR just adds toString() impl for EtsClassImpl, nothing more.

[github-actions]

Lifecycle test results

78 tests  ±0   78 ✅ ±0   1m 53s ⏱️ -3s
 7 suites ±0    0 💤 ±0 
 7 files   ±0    0 ❌ ±0 

Results for commit 0c36a60. ± Comparison against base commit 00164e3.

[github-actions]

Test results on JDK 19

   83 files  ±0     83 suites  ±0   27m 11s ⏱️ + 1m 27s
2 511 tests ±0  2 469 ✅ ±0  42 💤 ±0  0 ❌ ±0 
2 539 runs  ±0  2 497 ✅ ±0  42 💤 ±0  0 ❌ ±0 

Results for commit 0c36a60. ± Comparison against base commit 00164e3.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 59.53%. Comparing base (00164e3) to head (0c36a60).

Files	Patch %	Lines
...s/src/main/kotlin/org/jacodb/ets/model/EtsClass.kt	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                neo     #254      +/-   ##
============================================
- Coverage     59.53%   59.53%   -0.01%     
  Complexity     2238     2238              
============================================
  Files           309      309              
  Lines         18297    18298       +1     
  Branches       3261     3261              
============================================
  Hits          10894    10894              
- Misses         6329     6330       +1     
  Partials       1074     1074              

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[github-actions]

Test results on JDK 11

   83 files  ±0     83 suites  ±0   28m 55s ⏱️ -27s
2 511 tests ±0  2 471 ✅ ±0  40 💤 ±0  0 ❌ ±0 
2 539 runs  ±0  2 499 ✅ ±0  40 💤 ±0  0 ❌ ±0 

Results for commit 0c36a60. ± Comparison against base commit 00164e3.

[github-actions]

Test results on JDK 8

   83 files  ±0     83 suites  ±0   30m 4s ⏱️ + 1m 3s
2 511 tests ±0  2 466 ✅ ±0  45 💤 ±0  0 ❌ ±0 
2 539 runs  ±0  2 494 ✅ ±0  45 💤 ±0  0 ❌ ±0 

Results for commit 0c36a60. ± Comparison against base commit 00164e3.