Python 3.10 improvements (#1139)

## Description

Follow-up PR for #1133 but purely esthetic, no functional changes

Cleans up the code to make it more in comformance with Python 3.10
capabilities.

Replaces:
 - type `Union` with `|`
 - type `Dict`/`Set`/`List`/`Tuple` with `dict`/`set`/`list`/`tuple`
 - `Optional` with ` | None`
 - `if:` ... `elif`... -> `match`

Fixes: 
 - `gdb.events.*Event` -> `gdb.*Event`
- `GefHeapManager.malloc_align_address` had its `ceil` lambda moved as a
proper (nested) function

Lint:
 - `except:` -> `except Exception:`
 - removed a bunch of unused f-strings
 - `if not .. in ..` -> `if .. not in ..`
 - some short named variables renamed

.gitignore

@@ -14,3 +14,4 @@ debug.log
 htmlcov
 .benchmarks
 site/
+untracked/