Merge train: #488, #490-#494, #496, #497 plus index and parity sync

[rmorozov]

Before: eight open PRs each needed its own master merge and CI run to land.

After: one integration branch carries all of them, so one CI run covers the batch. Merging it with a merge commit marks each of the PRs below as merged.

Included, with the head merged:

• Value: store every integral type as int64_t, nullptr as None, refuse characters (0067) #493 Value constructors (4141138)
• parity: from-import of one name under two names (0155) #497 import alias (bbda244)
• Decode Python string-literal escapes (\x, \u, \U, octal, control letters) (0041) #490 string escapes (10c11e3)
• loop.cycle is a callable, not the integer 2 (0144) #488 loop.cycle callable (487c414)
• A dictsort pair reads as the 2-tuple (key, value) (0159) #492 dictsort pair (d8f7350)
• parity: sequence protocol follow-ups (0037) #496 sequence follow-ups (3426219)
• parity(0047): JSON null is None, undefined prints Undefined in containers #494 JSON null (b2a071a)
• docs(tasks): split 0038 lexical scoping into 0165-0167, file 0168/0169, add the approved plan #491 0038 plan and tasks 0165-0169 (752d241)
• docs: sync the task index and parity summary after 0156 #495 is replaced by a final commit here (task index and docs/parity.md regenerated: 1492 cases).

Conflicts resolved: test/parity/divergences/statements.txt (dropped the two 0144 lines #488 fixes, kept 0156 and the new 0038/0165/0168 lines) and test/binding/nlohmann_json_binding_test.cpp (kept both ArrayIteration from #489 and NullMemberIsNone from #494).

Checked locally on the combined tree (Debug, C++17): the full suite, the parity corpus and the fuzz regressions pass. CI is green on 06181c2, including all three MSVC jobs under the /W4 /WX flags from #478.

Roles: merge steward only (no verifier on the train; each member PR ran its own). One red push: the first head failed all three MSVC jobs with C4310 in #490's helpers_tests.cpp:57 (wchar_t(0x1F600) in an if constexpr branch under /WX); fixed in 06181c2 by comparing against L"\U0001F600".

🤖 Generated with Claude Code

https://claude.ai/code/session_01DTQTriEsFrrBgcYNKDUUF4

[rmorozov]

All three MSVC jobs failed on test/helpers_tests.cpp(57): error C2220 / warning C4310: cast truncates constant value. This is #490's new CompileEscapes test: wchar_t(0x1F600) sits in an if constexpr branch that MSVC still compiles with a 16-bit wchar_t, and /WX from #478 now rejects it. It is not red on master.

Fix pushed in 06181c2 to this train: the test now compares against the wide literal L"\U0001F600", which is a surrogate pair on MSVC and one code unit elsewhere. The helpers_tests suite passes locally. Waiting for the new CI run.

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