Refactor/tests

[MAfarrag]

Description

Normalize the package to lowercase, adopt snake_case naming conventions,
rename the GitHub organization, add multi-encoding D8 flow direction
support, and fix documentation build.

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Issues

• Fixes refactor(package): rename package from Hapi to hapi #170
• Fixes chore(org): rename organization from Serapieum-of-alex to serapeum-org #171
• Fixes refactor(routing): rename Routing methods to snake_case #172
• Fixes feature(dem): support SAGA and GRASS D8 flow direction encodings #173
• Fixes refactor(tests): reorganize test files to snake_case subdirectories #174
• Fixes docs(api): fix mkdocstrings directives from Hapi to hapi #175

How Has This Been Tested?

• 77 new unit tests for DEM.flow_direction_index covering all three
  D8 encodings (ESRI, SAGA, GRASS), validation, no-data handling,
  cross-encoding consistency, and edge cases.
• Full test suite passes: pixi run -e dev pytest -vvv -m "not fig_share"
• mkdocs build succeeds: pixi run -e docs mkdocs build

Checklist:

• updated version number in pyproject.toml
• updated environment.yml and the lock file
• added changes to History.rst
• updated the latest version in README file
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes