Allow multiple tracing/profile callbacks

[rogerbinns]

Currently there can only be one profiler, one authorizer, one collation needed callback etc.

This is especially problematic with the profiler because apswtrace needs it, but if any other code installs a tracer then apswtrace sees nothing.

The simplest approach would be to add a name parameter when they are registered/unregistered. The default is None. Internally APSW would keep a list for the callback and invoke the appropriate ones.

As an example the sqlite3_tracev2 would be a array of:

PyObject *name;
unsigned mask;
PyObject *callback;

Then when a trace event fires the list is traversed and any whose mask matches the event is called.

Some additional things:

• It is common to remove callbacks while in a callback, so mutating the list while iterating it must work. The simplest thing is to make name and callback be NULL on deletion an never resize the list to be smaller.
• Use PyObject_RichCompareBool with Py_EQ to see if name matches on register/unregister
• They should be included during tp_traverse

[rogerbinns]

Implemented for sqlite3_trace_v2 calls where I already had to handle thesqlite3_profile deprecation co-existence.

It doesn't make sense for auth - what if one callback says yes and one says no and one says ignore?

The progress callback might be useful, but I'll wait till someone asks.