Initial implementation of bank account

[oxisto]

This PR includes an initial implementation of a bank account, which holds cash. It also adds more transaction types (not all of them are functional yet) and includes a very basic calculation of the current cash to a portfolio snapshot.

[codecov]

Codecov Report

Attention: 15 lines in your changes are missing coverage. Please review.

Comparison is base (0e223b4) 86.23% compared to head (af8f0d9) 86.61%.
Report is 1 commits behind head on main.

❗ Current head af8f0d9 differs from pull request most recent head a1b5255. Consider uploading reports for the commit a1b5255 to get more accurate results

Files	Patch %	Lines
gen/account_sql.go	90.69%	3 Missing and 1 partial ⚠️
service/portfolio/transactions.go	71.42%	2 Missing and 2 partials ⚠️
service/portfolio/snapshot.go	50.00%	2 Missing and 1 partial ⚠️
finance/calculation.go	85.71%	2 Missing ⚠️
gen/portfolio.go	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #253      +/-   ##
==========================================
+ Coverage   86.23%   86.61%   +0.38%     
==========================================
  Files          20       23       +3     
  Lines        1024     1143     +119     
==========================================
+ Hits          883      990     +107     
- Misses         97      104       +7     
- Partials       44       49       +5     

Flag	Coverage Δ
unittests	86.61% <90.06%> (+0.38%)	⬆️

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