Allow symbolic scalars in linear combinations

[daxfohl]

Followup to #7003, allowing symbolic scalars in LinearCombinationOfGates and LinearCombinationOfOps.

Applies to #1617.

[codecov]

Codecov Report

Attention: Patch coverage is 96.15385% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.88%. Comparing base (0e50a8c) to head (6e31825).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cirq-core/cirq/linalg/operator_spaces.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7030      +/-   ##
==========================================
- Coverage   97.89%   97.88%   -0.01%     
==========================================
  Files        1085     1085              
  Lines       95188    95199      +11     
==========================================
+ Hits        93181    93190       +9     
- Misses       2007     2009       +2     

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[daxfohl]

@pavoljuhas is there a workaround for the coverage check on

if typechecking:
    import cirq```?

[pavoljuhas]

LGTM with a tiny adjustment to typing. I will take a look at the coverage noise separately.
Thanks for adding this!

[pavoljuhas]

@pavoljuhas is there a workaround for the coverage check on

if typechecking:
    import cirq```?

This gets fixed by moving coverage configuration to pyproject.toml - #7038 (comment)