Invalidate context state during cleanup

[arajkumar]

Currently, when switching between modes, the follow process cleans up context files, which include details like WAL segment size and timeline. However, we haven't been resetting the in-memory state that decides whether the context should be read from these files. This can lead to the usage of outdated timeline information while retriving the context[1][2][3].

This commit addresses this issue by resetting the in-memory state during context cleanup. This ensures that the system will re-read the context from the files after any cleanup, leading to more accurate and reliable timeline information.

[1]

pgcopydb/src/bin/pgcopydb/ld_transform.c

Lines 201 to 212 in 8d305a5

	/* we need timeline and wal_segment_size to compute WAL filenames */
	if (specs->system.timeline == 0)
	{
	if (!stream_read_context(&(specs->paths),
	&(specs->system),
	&(specs->WalSegSz)))
	{
	log_error("Failed to read the streaming context information "
	"from the source database, see above for details");
	return false;
	}
	}

[2]

pgcopydb/src/bin/pgcopydb/follow.c

Lines 428 to 438 in 8d305a5

	if (streamSpecs->system.timeline == 0)
	{
	if (!stream_read_context(&(streamSpecs->paths),
	&(streamSpecs->system),
	&(streamSpecs->WalSegSz)))
	{
	log_error("Failed to read the streaming context information "
	"from the source database, see above for details");
	return false;
	}
	}

[3]

pgcopydb/src/bin/pgcopydb/ld_apply.c

Lines 206 to 216 in 8d305a5

	if (specs->system.timeline == 0)
	{
	if (!stream_read_context(&(specs->paths),
	&(specs->system),
	&(specs->WalSegSz)))
	{
	log_error("Failed to read the streaming context information "
	"from the source database, see above for details");
	return false;
	}
	}