fix: repair the litestar and faststream floors

[lesnik512]

The two decayed floors found by the composition check in #218. Neither was a simple bump: each
turned out to rest on a dependency the upstream package uses but does not declare.

litestar>=2.19                              # was >=2.15
typing-extensions>=4.12                     # new, litestar extra
pydantic>=2.12; python_version >= '3.14'    # new, faststream extra
typing-extensions>=4.12.2                   # new, faststream extra

litestar

litestar/concurrency.py:8 does import sniffio. Until 2.19 litestar did not declare it and it
arrived through anyio, which dropped the dependency in 4.14. litestar==2.15.0 with
anyio==4.14.2 therefore raises ModuleNotFoundError: No module named 'sniffio' at
import lite_bootstrap. 2.19.0 is the first release declaring sniffio>=1.3.1.

Raising the floor exposed a second undeclared dependency underneath it: every litestar from 2.19 to
2.24 declares typing-extensions bare, while importing typing_extensions.ReadOnly (4.9). With
typing-extensions pinned at this project's own floor, the resolver has no reason to lift it, so the
floor has to be declared here:

typing-extensions	3.10	3.14
4.9.0, 4.11.0	pass	AttributeError: attribute '__default__' of 'typing.ParamSpec' objects is not writable
4.12.0	pass	pass

4.9 is enough for ReadOnly, but 4.9 and 4.11 assign typing.ParamSpec.__default__, which Python
3.13 made read-only. Hence >=4.12 rather than >=4.9.

faststream

faststream>=0.6 pulls fast-depends[pydantic], which allows pydantic>=1.7.4,<3.0.0. pydantic
requires typing-extensions>=4.12.2 on 3.13+, so with typing-extensions pinned at 4.8 (this
project's floor, lifted by faststream's own typing-extensions>=4.8.0) the resolver walks pydantic
back to 2.7.4, whose pydantic-core==2.18.4 builds against pyo3 0.21.2 and has no cp313 or cp314
wheel. The reported 3.14 failure was the same defect on 3.13, one interpreter earlier than #218 said.

Raising the faststream floor does not help: 0.7.5 still declares only fast-depends[pydantic]>=3.0.0,
and fast-depends 3.0.8 is the newest release. The constraint has to come from here.

typing-extensions>=4.12.2 fixes 3.10 through 3.13, landing pydantic 2.11.10. On 3.14 pydantic 2.11
still has no wheel, and 2.12 is the first that does, so that one is declared under a marker rather
than as a floor for every interpreter where 2.7.4 is fine.

Why these sit on the extras rather than on core

Both are constraints on packages lite-bootstrap never imports, declared because the chain that
reaches them is under-constrained upstream. Putting typing-extensions>=4.12.2 in
[project.dependencies] instead would be one line rather than four and would fix both, but it would
overstate core: #214 measured bare core at 4.6, and free-all still resolves 4.6.0 after this change.
Keeping the constraint where its cause is keeps the core claim honest and lets each comment name what
forced it. Worth a second opinion in review, since the alternative is genuinely simpler.

Verification

Every *-all extra under --resolution lowest-direct, on every supported interpreter, installed and
bootstrapped:

extra	3.10	3.11	3.12	3.13	3.14
free-all	ok	ok	ok	ok	ok
fastapi-all	ok	ok	ok	ok	ok
litestar-all	ok	ok	ok	ok	ok
faststream-all	ok	ok	ok	ok	ok
fastmcp-all	ok	ok	ok	ok	ok

25 of 25, against 8 of 10 before. litestar-all and faststream-all additionally bootstrap and tear
down their bootstrapper, not just import.

just lint-ci and just test-ci pass (277 passed, 100% coverage). uv.lock is unchanged.