fix: Correctly display unrequested environments on task list (prefi…

…x-dev#2402)

Description

**Issue**:
- explicitly requesting tasks for a specific environment with the
`--environment` flag, along with the `--summary (-s)` flag, would also
display tasks available in other environments.

<details>
  
  <summary> before fix: </summary>

  current `pixi task ls --summary` 


![image](https://github.com/user-attachments/assets/a7fc008f-6d85-46c6-a3b6-434941c5ba38)
  

![image](https://github.com/user-attachments/assets/c8b20ad8-5515-426c-a683-4e0e89f4f22e)

  
</details>

**Fix**:

- A new `env_task_map` was introduced, which either maps the explicitly
requested environment (if specified) or iterates over all environments,
filtering based on platform compatibility.
- Removed the `get_tasks_per_env` function, but could extract the new
logic back out into it
- Tried to prevent iterating over `projects.environments()` again 
 

<details>

  <summary> after fix: </summary>
  regular `task ls --summary` still works:
  

![image](https://github.com/user-attachments/assets/7e1c3402-328b-4606-b1d4-89a638d5f98c)

  

![image](https://github.com/user-attachments/assets/8c3df61f-84a9-4877-ae5c-c2994e91cc15)
  
  `pixi task ls` with no args unaffected:
  

![image](https://github.com/user-attachments/assets/744fbb34-5a05-4bc2-b22d-b630eb0a91ac)


</details>

src/cli/task.rs

@@ -267,25 +267,6 @@ fn list_tasks(
     Ok(())
 }
 
-fn get_tasks_per_env(
-    task_list: HashSet<TaskName>,
-    environments: Vec<Environment>,
-) -> HashMap<Environment, HashMap<TaskName, Task>> {
-    let mut tasks_per_env: HashMap<Environment, HashMap<TaskName, Task>> = HashMap::new();
-    for env in environments {
-        let mut tasks: HashMap<TaskName, Task> = HashMap::new();
-        let this_env_tasks = env.tasks(Some(env.best_platform())).unwrap_or_default();
-        for taskname in task_list.iter() {
-            // if the task is in the environment, add it to the list
-            if let Some(&task) = this_env_tasks.get(taskname) {
-                tasks.insert(taskname.clone(), task.clone());
-            }
-        }
-        tasks_per_env.insert(env, tasks);
-    }
-    tasks_per_env
-}
-
 pub fn execute(args: Args) -> miette::Result<()> {
     let mut project = Project::load_or_else_discover(args.project_config.manifest_path.as_deref())?;
     match args.operation {
@@ -397,20 +378,30 @@ pub fn execute(args: Args) -> miette::Result<()> {
                         .ok_or_else(|| miette::miette!("unknown environment '{n}'"))
                 })
                 .transpose()?;
-            let available_tasks: HashSet<TaskName> =
+
+            let env_task_map: HashMap<Environment, HashSet<TaskName>> =
                 if let Some(explicit_environment) = explicit_environment {
-                    explicit_environment.get_filtered_tasks()
+                    HashMap::from([(
+                        explicit_environment.clone(),
+                        explicit_environment.get_filtered_tasks(),
+                    )])
                 } else {
                     project
                         .environments()
-                        .into_iter()
-                        .filter(|env| {
-                            verify_current_platform_has_required_virtual_packages(env).is_ok()
+                        .iter()
+                        .filter_map(|env| {
+                            if verify_current_platform_has_required_virtual_packages(env).is_ok() {
+                                Some((env.clone(), env.get_filtered_tasks()))
+                            } else {
+                                None
+                            }
                         })
-                        .flat_map(|env| env.get_filtered_tasks())
                         .collect()
                 };
 
+            let available_tasks: HashSet<TaskName> =
+                env_task_map.values().flatten().cloned().collect();
+
             if available_tasks.is_empty() {
                 eprintln!("No tasks found",);
                 return Ok(());
@@ -426,7 +417,20 @@ pub fn execute(args: Args) -> miette::Result<()> {
                 return Ok(());
             }
 
-            let tasks_per_env = get_tasks_per_env(available_tasks, project.environments());
+            let tasks_per_env = env_task_map
+                .into_iter()
+                .map(|(env, task_names)| {
+                    let tasks: HashMap<TaskName, Task> = task_names
+                        .into_iter()
+                        .filter_map(|task_name| {
+                            env.task(&task_name, None)
+                                .ok()
+                                .map(|task| (task_name, task.clone()))
+                        })
+                        .collect();
+                    (env, tasks)
+                })
+                .collect();
 
             list_tasks(tasks_per_env, args.summary).expect("io error when printing tasks");
         }