Add a comman table property to the sequencer class

[tobiasah]

Often a command table is associated with a specific sequencer code. This commit simplt adds a property as a "storage" in the sequencer class for a command table. There is no logic attached to this other then storing.

Description:

Fixes issue: #

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 (e082c54) 99.61% compared to head (0f64d72) 99.60%.

❗ Current head 0f64d72 differs from pull request most recent head 3a39c4f. Consider uploading reports for the commit 3a39c4f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #268      +/-   ##
==========================================
- Coverage   99.61%   99.60%   -0.01%     
==========================================
  Files          40       40              
  Lines        2567     2560       -7     
==========================================
- Hits         2557     2550       -7     
  Misses         10       10              

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

... and 1 file with indirect coverage changes

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