Fixed dijkstra implementation bug: improved time from exponential to O(E * logV)

[taaae]

Description

The previous implementation incorrectly defined prio as BTreeMap<V, E>, causing this line:
while let Some((vertex, path_weight)) = prio.pop_first() {
to select elements with the smallest vertex instead of the smallest path_weight potentially leading to exponential time complexity.
I replaced BTreeMap<V, E> with BTreeSet<(E, V)> and added code to remove old entries, which was missing in the previous implementation using heap: #162

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I ran bellow commands using the latest version of rust nightly.
• I ran cargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• I ran cargo fmt just before my last commit.
• I ran cargo test just before my last commit and all tests passed.
• I added my algorithm to the corresponding mod.rs file within its own folder, and in any parent folder(s).
• I added my algorithm to DIRECTORY.md with the correct link.
• I checked COUNTRIBUTING.md and my code follows its guidelines.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.47%. Comparing base (7903120) to head (33b2a33).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #848   +/-   ##
=======================================
  Coverage   95.47%   95.47%           
=======================================
  Files         316      316           
  Lines       22932    22934    +2     
=======================================
+ Hits        21895    21897    +2     
  Misses       1037     1037           

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