Revert `mount_path` parameter from `FastMCP` #125

Job	Run time
checks / pre-commit	35s
checks / readme-snippets	11s
checks / test (3.10, locked, ubuntu-latest)	46s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 9s
checks / test (3.11, locked, ubuntu-latest)	48s
checks / test (3.11, locked, windows-latest)	2m 29s
checks / test (3.12, locked, ubuntu-latest)	49s
checks / test (3.10, lowest-direct, ubuntu-latest)	44s
checks / test (3.12, lowest-direct, ubuntu-latest)	51s
checks / test (3.13, lowest-direct, windows-latest)	2m 19s
checks / test (3.12, lowest-direct, windows-latest)	4m 1s
checks / test (3.11, lowest-direct, windows-latest)	2m 27s
checks / test (3.12, locked, windows-latest)	3m 24s
checks / test (3.10, lowest-direct, windows-latest)	2m 39s
checks / test (3.14, lowest-direct, windows-latest)	2m 21s
checks / test (3.13, lowest-direct, ubuntu-latest)	42s
checks / test (3.10, locked, windows-latest)	2m 17s
checks / test (3.13, locked, ubuntu-latest)	45s
checks / test (3.11, lowest-direct, ubuntu-latest)	48s
checks / test (3.14, locked, windows-latest)	3m 58s
checks / test (3.13, locked, windows-latest)	3m 3s
checks / test (3.14, locked, ubuntu-latest)	2m 16s
all-green	5s
	39m 27s

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