FIX: Duplicate names in tree_namespace

[ZLLentz]

Description

If we're constructing the tree namespace and we encounter a leaf that already exists, we need to handle it properly. Currently it can fail and break the tree. This makes it show a warning message about two devices having a naming conflict.

Motivation and Context

xcspython load has a conflict between xcs_lodcm and xcs_lodcm_yag

How Has This Been Tested?

I have added a test.

[codecov-io]

Codecov Report

Merging #128 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #128      +/-   ##
==========================================
+ Coverage   97.17%   97.18%   +<.01%     
==========================================
  Files          15       15              
  Lines         779      781       +2     
==========================================
+ Hits          757      759       +2     
  Misses         22       22

Impacted Files	Coverage Δ
hutch_python/namespace.py	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update de702a5...14afcd0. Read the comment docs.

[ZLLentz]

@teddyrendahl thoughts on if this should fail silently or noisily?

[ZLLentz]

I have opted to make this a WARNING message about two devices having a naming conflict. You can proceed into a session as normal, but I don't make any guarantees about the tree namespace being well-formed if there is a naming conflict.