Fix some Pyright type errors in Span/ReadableSpan and utility stubs

[emdneto]

Errors:

opentelemetry-sdk/src/opentelemetry/sdk/trace/init.py:145:59 - error: Function with declared return type "bool" must return value on all code paths "None" is not assignable to "bool" (reportReturnType)
opentelemetry-sdk/src/opentelemetry/sdk/trace/init.py:255:40 - error: Object of type "None" cannot be called (reportOptionalCall)
opentelemetry-sdk/src/opentelemetry/sdk/trace/init.py:864:28 - error: Argument of type "int | None" cannot be assigned to parameter "maxlen" of type "int" in function "init" Type "int | None" is not assignable to type "int" "None" is not assignable to "int" (reportArgumentType)
opentelemetry-sdk/src/opentelemetry/sdk/trace/init.py:868:32 - error: Argument of type "int | None" cannot be assigned to parameter "maxlen" of type "int" in function "init" Type "int | None" is not assignable to type "int" "None" is not assignable to "int" (reportArgumentType)
opentelemetry-sdk/src/opentelemetry/sdk/trace/init.py:881:37 - error: Argument of type "int | None" cannot be assigned to parameter "maxlen" of type "int" in function "from_seq" Type "int | None" is not assignable to type "int" "None" is not assignable to "int" (reportArgumentType)
opentelemetry-sdk/src/opentelemetry/sdk/trace/init.py:883:9 - error: Method "get_span_context" overrides class "Span" in an incompatible manner Return type mismatch: base method returns type "SpanContext", override returns type "SpanContext | None" Type "SpanContext | None" is not assignable to type "SpanContext" "None" is not assignable to "SpanContext" (reportIncompatibleMethodOverride)
opentelemetry-sdk/src/opentelemetry/sdk/trace/init.py:1050:49 - error: "name" is not a known attribute of "None" (reportOptionalMemberAccess)
opentelemetry-sdk/src/opentelemetry/sdk/trace/init.py:1245:23 - error: Argument of type "Sequence[Link] | None" cannot be assigned to parameter "links" of type "Sequence[Link]" in function "init" Type "Sequence[Link] | None" is not assignable to type "Sequence[Link]" "None" is not assignable to "Sequence[Link]" (reportArgumentType)
8 errors, 0 warnings, 0 informations