lower the python floor to 3.12

Fixes #26.

`requires-python` was `>=3.14`. On anything older poetry declines to create an
environment, and it says so on stderr while leaving stdout empty. The README
tells the user to run `iex (poetry env activate)`, `iex` only sees stdout, and
PowerShell reports

    Invoke-Expression : Cannot bind argument to parameter 'Command' because it
    is null.

which points at `iex` rather than at the install that never happened. The
first reply on the issue guessed the reporter was missing `iex`, which is a
built-in alias, so the error is actively misleading.

3.14 looks stricter than anything the code needs. Every file in src/ compiles
on 3.10, no 3.13 or 3.14 only syntax appears anywhere in the tree, and the
full task set was run end to end on 3.12.10 against a live account with all
six tasks completing. The dependency graph agrees: numpy is the highest floor
in the lock at >=3.12, so 3.12 is where the real constraint sits.

Verified after the change on 3.12.10: `poetry install` creates the
environment, `poetry env activate` emits a real activation command instead of
nothing, `iex (poetry env activate)` activates in PowerShell, and every
dependency plus every module under src/ imports.

The lock is regenerated rather than left stale, since `requires-python` feeds
its content hash. The only substantive change is a typing_extensions marker
for python_version < 3.13; the package set is unchanged at 203. Regenerated
with poetry 2.4.1 to match the version that wrote the existing file.

The README gains the version bump and a short note on the failure, so anyone
who hits it while running an older Python can recognise it.

pyproject.toml

@@ -6,7 +6,7 @@ authors = [
     {name = "Carl Furtado",email = "user0332@duck.com"}
 ]
 license = "MIT"
-requires-python = ">=3.14"
+requires-python = ">=3.12"
 dependencies = [
     "selenium (>=4.46.0,<5.0.0)",
     "matplotlib (>=3.11.1,<4.0.0)",