refactor: move streamable HTTP app creation from FastMCP to lowlevel Server #165

Job	Run time
checks / pre-commit	35s
checks / readme-snippets	12s
checks / test (3.11, lowest-direct, ubuntu-latest)	48s
checks / test (3.12, lowest-direct, windows-latest)	3m 25s
checks / test (3.10, lowest-direct, ubuntu-latest)	49s
checks / test (3.13, locked, ubuntu-latest)	42s
checks / test (3.12, lowest-direct, ubuntu-latest)	51s
checks / test (3.11, locked, windows-latest)	2m 32s
checks / test (3.13, lowest-direct, windows-latest)	2m 27s
checks / test (3.11, locked, ubuntu-latest)	48s
checks / test (3.12, locked, windows-latest)	3m 32s
checks / test (3.10, lowest-direct, windows-latest)	2m 42s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 12s
checks / test (3.13, locked, windows-latest)	2m 25s
checks / test (3.12, locked, ubuntu-latest)	50s
checks / test (3.14, locked, windows-latest)	3m 19s
checks / test (3.11, lowest-direct, windows-latest)	2m 43s
checks / test (3.13, lowest-direct, ubuntu-latest)	45s
checks / test (3.14, locked, ubuntu-latest)	2m 21s
checks / test (3.10, locked, windows-latest)	2m 33s
checks / test (3.14, lowest-direct, windows-latest)	2m 15s
checks / test (3.10, locked, ubuntu-latest)	46s
all-green	2s
	38m 34s

Provide feedback