Co-authored-by: Mahe Iram Khan <65779580+ForgottenProgramme@users.noreply.github.com>

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Co-authored-by: jaimergp <jaimergp@users.noreply.github.com>

- Introduced `is_url` and `expand` functions for improved URL normalization and path expansion.
- Updated logic to handle file paths and URLs consistently, ensuring compatibility with existing specifications.
- Added validation for URL format using regex, maintaining backward compatibility while improving parsing accuracy.

- Removed the ExplicitEnvironment class and integrated its functionality into the Environment class.
- Updated the Dependencies class to include an explicit marker for environments created from @explicit files.
- Adjusted the conda installer and requirements specifications to work with the new Environment structure.
- Modified tests to reflect changes in the environment handling, ensuring compatibility with explicit specifications.

…cations

- Replaced the ExplicitRequirementsSpec with a unified RequirementsSpec that handles both regular and explicit requirements files.
- Updated the reading logic to utilize a generator for improved efficiency and clarity.
- Adjusted tests to reflect the new unified handling of requirements, ensuring compatibility with explicit specifications.
- Removed deprecated functions and streamlined the codebase for better maintainability.

- Integrated explicit environment handling directly into the install function, removing the need for a separate _install_explicit_environment function.
- Enhanced logging to provide detailed feedback on the source of package specifications used during installation.
- Improved the logic for determining package specs by prioritizing original files, provided specs, and environment dependencies.
- Ensured compatibility with the latest requirements handling and streamlined the installation process for explicit environments.

- Removed the _execute_transaction function and integrated its logic directly into the install function.
- Enhanced the transaction handling by checking for 'nothing to do' before executing.
- Streamlined the process of downloading, extracting, and executing transactions, improving clarity and maintainability.

Co-authored-by: jaimergp <jaimergp@users.noreply.github.com>

…ror if no solver backend is found.

…ng for better performance and readability.

- Removed unnecessary comments and improved the `yield_lines` function in `read.py` for cleaner code.

- Introduced `test_explicit_marker_in_middle` to verify functionality of the @explicit marker when placed in the middle of the dependency list.
- Added `test_explicit_marker_at_end` to ensure the @explicit marker works correctly when positioned at the end of the dependencies.

- Updated the `explicit` function to track user-requested specs separately from all packages, preventing dependencies from polluting the user's request history.
- Added type hints for parameters in `explicit`, `_solve`, `dry_run`, and `install` functions to improve code clarity and type checking.
- Modified test cases to ensure correct handling of the `@EXPLICIT` marker in various positions within the dependency list.

- Removed redundant fixture and consolidated tests for explicit environments.
- Added new tests to verify the detection of explicit dependencies and the handling of the @explicit marker in various positions within the dependency list.
- Improved type hinting for test functions and ensured consistent assertions for environment properties.

- Updated assertions in `test_explicit_file_spec_is_registered` to improve readability and ensure correct handling of dependencies.
- Replaced direct access to `env.dependencies["conda"]` with a more general approach using `env.dependencies.raw`, enhancing flexibility in dependency checks.

…it-env-spec