Fix cmake config file to use @package_nspace@

[martinmoene]

See span-lite PR 77.

File ./cmake/{prj}-config.cmake.in:

if( NOT TARGET @package_nspace@::@package_name@ )

Plan:

• lest (NA)
• active-lite
• any-lite
• atomic-lite
• bit-lite
• boolean-lite
• byte-lite
• expected-lite
• invoke-lite
• jthread-lite
• observer-ptr-lite
• optional-bare
• optional-lite
• optional-fun-lite
• ring-span-lite
• scope-lite
• span-lite (original PR)
• status-value-lite
• string-lite
• string-view-lite
• type-lite
• value-ptr-lite
• variant-lite
• nonstd-lite-project

Other:

• rpc-lite