Update sql queries and extend mutation color palette

[johausmann]

• Updated raw SQL queries in queries.py to use SQLAlchemy text clause object and parameter substitution via placeholders.
• Enhanced color palette for mutation statistics plots (inherited from ColorBrewer palette used previously).

[codecov]

Codecov Report

Base: 83.21% // Head: 83.21% // No change to project coverage 👍

Coverage data is based on head (ac46a7d) compared to base (5185585).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop      #87   +/-   ##
========================================
  Coverage    83.21%   83.21%           
========================================
  Files           46       46           
  Lines         4218     4218           
========================================
  Hits          3510     3510           
  Misses         708      708           

Impacted Files	Coverage Δ
covigator/dashboard/figures/__init__.py	100.00% <ø> (ø)
covigator/dashboard/figures/mutation_stats.py	70.96% <ø> (ø)
covigator/database/queries.py	70.12% <100.00%> (ø)

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