: logging: default disable log forwarding

Summary:
this diff sets the following defaults for hyperactor-mesh global configuration values:
- `MESH_ENABLE_LOG_FORWARDING=false`
- `MESH_ENABLE_FILE_CAPTURE=false`
- `MESH_TAIL_LOG_LINES=0`

the effect of this is to disable log forwarding, prevent allocating resources for log forwarding, no file capture at the hyperactor mesh level (including no "exit tail" capture), in fact, under these defaults there is no interception of child process stdio at all.

a workplace post is planned to announce this change in default configuration.

this diff is built on: D85783397 provide config for enabling/disabling hyperactor-mesh logging interception features, D85919326 for avoiding spinning up `LogForwardActor` meshes when log forwarding is enabled and D85969320 for some detailed testing.

Differential Revision: D86994420

Author: shayne-fletcher

hyperactor_mesh/src/bootstrap.rs

@@ -99,7 +99,7 @@ declare_attrs! {
         env_name: Some("HYPERACTOR_MESH_ENABLE_LOG_FORWARDING".to_string()),
         py_name: None,
     })
-    pub attr MESH_ENABLE_LOG_FORWARDING: bool = true;
+    pub attr MESH_ENABLE_LOG_FORWARDING: bool = false;
 
     /// When `true`: if stdio is piped, each child's `StreamFwder`
     /// also forwards lines to a host-scoped `FileAppender` managed by
@@ -124,7 +124,7 @@ declare_attrs! {
         env_name: Some("HYPERACTOR_MESH_ENABLE_FILE_CAPTURE".to_string()),
         py_name: None,
     })
-    pub attr MESH_ENABLE_FILE_CAPTURE: bool = true;
+    pub attr MESH_ENABLE_FILE_CAPTURE: bool = false;
 
     /// Maximum number of log lines retained in a proc's stderr/stdout
     /// tail buffer. Used by [`StreamFwder`] when wiring child
@@ -133,7 +133,7 @@ declare_attrs! {
         env_name: Some("HYPERACTOR_MESH_TAIL_LOG_LINES".to_string()),
         py_name: None,
     })
-    pub attr MESH_TAIL_LOG_LINES: usize = 100;
+    pub attr MESH_TAIL_LOG_LINES: usize = 0;
 
     /// If enabled (default), bootstrap child processes install
     /// `PR_SET_PDEATHSIG(SIGKILL)` so the kernel reaps them if the