Add typechecking to the Jaeger propagator (#5440)

* Fix return type annotation of _parse_trace_id_header in Jaeger propagator

The function returns a 3-tuple (trace_id, span_id, flags) on every code
path and callers unpack three values, but the annotation declared
tuple[int] (a one-element tuple), which misleads type checkers.

* Add changelog fragment for #5440

* Fix remaining typing issues in Jaeger propagator and enable typechecking

Parameterize Getter/Setter with CarrierT to match the base class
signatures, guard against None baggage values before unquoting, type
header values as str instead of the unbound CarrierT, and make
_int_from_hex_str return int | None with explicit fallbacks at the call
sites. Add the package to the pyright include list.

* Add test for empty baggage value in Jaeger propagator

* Annotate parent as SpanContext | None in Jaeger propagator inject