Remove ct validation when active validation is disabled (#269)

[markheik]

Description:

To improve CommandTable creation and usage, do not validate it during as_dict().

Introduces is_valid() method compensate for optional validation.

Removed unnecessary deepcopy of schemas for speed improvement

The following script is 10x faster than with copying:

for i in range(100):
      ct.table[i].waveform.index = I

Fixes issue: #269

Checklist:

• Add tests for the change to show correct behavior.
• Add or update relevant docs, code and examples.
• Update CHANGELOG.rst with relevant information and add the issue number.
• Add .. versionchanged:: where necessary.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7e7bccb) 99.60% compared to head (c610f09) 99.61%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #271   +/-   ##
=======================================
  Coverage   99.60%   99.61%           
=======================================
  Files          40       40           
  Lines        2552     2567   +15     
=======================================
+ Hits         2542     2557   +15     
  Misses         10       10           

Files	Coverage Δ
src/zhinst/toolkit/command_table.py	100.00% <100.00%> (ø)

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