Add ric lookup, separate into own files

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[codecov-commenter]

Codecov Report

Merging #245 (5d5c426) into main (776492c) will increase coverage by 0.03%.
The diff coverage is 77.77%.

@@            Coverage Diff             @@
##             main     #245      +/-   ##
==========================================
+ Coverage   69.35%   69.38%   +0.03%     
==========================================
  Files         107      109       +2     
  Lines        6200     6213      +13     
  Branches      492      492              
==========================================
+ Hits         4300     4311      +11     
- Misses       1783     1785       +2     
  Partials      117      117              

Impacted Files	Coverage Δ
pyEX/client.py	56.99% <ø> (ø)
pyEX/refdata/symbols.py	80.99% <ø> (+0.83%)	⬆️
pyEX/tests/test_api.py	100.00% <ø> (ø)
pyEX/tests/test_api_client.py	92.40% <ø> (ø)
pyEX/refdata/isin.py	75.00% <75.00%> (ø)
pyEX/refdata/ric.py	75.00% <75.00%> (ø)
pyEX/refdata/__init__.py	100.00% <100.00%> (ø)

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