Restructure `src/` using namespaces and add setup script

[dcajal]

Description:

To improve modularity, avoid naming collisions, and enable clean usage, we will reorganize the library into a namespace using MATLAB’s +folder convention.

New folder structure:

src/
└── +biosigmat/
    ├── +ecg/
    ├── +ppg/
    ├── +tools/

Why use namespaces:

• Prevents name conflicts with other functions or toolboxes.
• Allows scoped imports like import biosigmat.ppg.*.
• Improves autocompletion and structure within MATLAB IDE.
• Cleaner API and easier maintainability.

User workflow (to be included in the README):

% Step 1: Add the namespace root to the path
addpath('path/to/biosigmat/src/+biosigmat')

% Step 2 (optional): Import specific modules
import biosigmat.ecg.*

Setup automation:

We will provide a biosigmat_setup.m script in the root folder that:

• Automatically adds src/+biosigmat to the MATLAB path.
• Can be added to the user’s startup.m for permanent use.

Example script:

function biosigmat_setup()
    src_path = fullfile(fileparts(mfilename('fullpath')), 'src', '+biosigmat');
    fprintf('biosigmat loaded from: %s\n', src_path);
end

Tasks:

• Rename folders inside src/ to +ecg, +ppg, +tools, etc.
• Wrap all of them under a +biosigmat/ namespace.
• Update internal function calls if path-dependent.
• Add biosigmat_setup.m to the root of the repo.
• Update README to include setup instructions and optional use in startup.m:

% In startup.m
run('path/to/biosigmat/biosigmat_setup.m');