Give every member of AngouriMath.Extensions a worked, executed example (#585, #746 item 4) (#1029)

* Give every member of AngouriMath.Extensions a worked example (#585)

All 89 public members of the namespace carried a <summary> and none carried an
<example>, which is the whole of the library's second-largest public surface with
nothing showing what a member is for. Each now has one, and each is a case where
the answer is worth seeing rather than a restatement of the signature: that
substituting a pair of variables is sequential and so does not swap them, that
0.1 as a double converts to the binary value it actually holds and as a decimal
to 1/10, that the two one-sided limits of 1/x at zero differ and NaN is therefore
the claim that the two-sided one does not exist, that an integral with no
elementary antiderivative comes back as its own node.

A documented output is a promise the repository makes, so none of these is typed
from memory: ExtensionsExampleTest asserts every one of them against the value
the member returns, all 89 pinned by 59 facts. A change of answer now fails a
test rather than leaving a wrong claim standing in the XML docs.

Two of the three files are generated, so the examples go into the generator and
the file is regenerated from it: the interval and equation-system templates carry
a printed-value sample per type, and CompilationExtensions.tt computes its
example from the arity it is emitting. Regenerating AdditionalExtensions.cs also
restores the "this file is auto-generated" banner it had lost, and brings the
EquationSystemFunctionPattern template back in step with the Matrix return type
the file has had since Tensor was renamed.

No behaviour changes; the only executable code added is the test.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bjumi5K7fg8yx6UK1mZTQd

* Date the new test file to the year it was written

Sources/.editorconfig pins the header per directory, so a new file needs its
own scope or it ships with a copyright four years out of date.

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: Rafael-SOWNet

Sources/.editorconfig

@@ -90,4 +90,5 @@ file_header_template=\nCopyright (c) 2019-2026 Angouri.\nAngouriMath is licensed
 
 [Tests/AotSmokeTest/*.cs]
 [Tests/UnitTests/Algebra/SolveTest/CalculusEquationTest.cs]
+[Tests/UnitTests/Convenience/ExtensionsExampleTest.cs]
 file_header_template=\nCopyright (c) 2019-2026 Angouri.\nAngouriMath is licensed under MIT.\nDetails: https://github.com/asc-community/AngouriMath/blob/master/LICENSE.md.\nWebsite: https://am.angouri.org.\n