Bus merging logic to ensure correct bus type updates

[jbarberia]

Proposed fix for #935 and #936.

This update addresses an issue with the bus merging logic to ensure the resulting bus_type is correctly updated when buses are merged.

When two buses are connected by a switch or a zero-impedance line, the merged bus should have the highest priority bus_type (PQ=1, PV=2, Slack=3)

Changes Introduced

• Correctly updates the bus_type of the resulting bus to reflect the highest priority among the merged buses.
• Adds safeguards to prevent assigning invalid bus types (e.g., type 4).

[odow]

Reverting the name change. I addressed it separately in #959

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.71%. Comparing base (8824212) to head (48b8399).
Report is 10 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #937   +/-   ##
=======================================
  Coverage   93.71%   93.71%           
=======================================
  Files          43       43           
  Lines        9636     9638    +2     
=======================================
+ Hits         9030     9032    +2     
  Misses        606      606           

Files with missing lines	Coverage Δ
src/core/data.jl	90.82% <100.00%> (+0.01%)	⬆️

... and 3 files with indirect coverage changes

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