Fix unexpected markdown syntax in docstring

[ToastCheng]

In the docstring of ArithmeticGate.apply,
two exponentiation ** accidentally combine to a bold text syntax.
Here we add backtick quotes to avoid this, and also fix a few other
similar instances.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.37%. Comparing base (7673240) to head (cbeca32).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7653      +/-   ##
==========================================
- Coverage   99.37%   99.37%   -0.01%     
==========================================
  Files        1080     1080              
  Lines       96378    96378              
==========================================
- Hits        95775    95774       -1     
- Misses        603      604       +1     

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[pavoljuhas]

Please see the inline comment. Also, I found a few more places which show the same mix-up between the literal ** and a bold-face rendering in Cirq web docs.

Can you please fix these with double-backticks as well?

Cirq/cirq-core/cirq/ops/common_gates.py

Line 394 in 7673240

written as X**a Z**b for a,b=0,1,...,d-1. For a qubit, there is only one

Cirq/cirq-core/cirq/ops/pauli_string_phasor.py

Lines 75 to 78 in 7673240

	exponent_neg: How much to phase vectors in the negative eigenspace,
	in the form of the t in (-1)**t = exp(i pi t).
	exponent_pos: How much to phase vectors in the positive eigenspace,
	in the form of the t in (-1)**t = exp(i pi t).

Cirq/cirq-core/cirq/ops/pauli_string_phasor.py

Lines 295 to 298 in 7673240

	exponent_neg: How much to phase vectors in the negative eigenspace,
	in the form of the t in (-1)**t = exp(i pi t).
	exponent_pos: How much to phase vectors in the positive eigenspace,
	in the form of the t in (-1)**t = exp(i pi t).

[pavoljuhas]

Please use double backticks instead, ie, ``5 % 2**2 = 1``, to avoid having ** interpreted as a bold-face markdown.
2^2 is a valid XOR expression which may confuse readers.

[ToastCheng]

Done, thanks for pointing this out!

[pavoljuhas]

Thank you for fixing this!

[pavoljuhas]

I am updating the initial comment as it will become the merge commit message.
Here is the original PR description for reference:

---

In the docstring of ArithmeticGate.apply, two exponentiation ** accidentally combine to a bold text syntax. This PR changes ** to ^ to avoid this.

Note that my first attempt is to make it an inline latex expression, however the spacing of % looks a bit weird:

I could add some space, but that will make the expression even more difficult to read in source code (e.g. $-2\ \%\ 2^3 = 6$), so in the end I just use ^ instead as it's also being used in the rest of the documentation.