Initial commit: snapshot of spesmilo/electrumx 2.0.0

Unmodified source tree of upstream commit 280cb339aa158e099eb936033eecd15719770651
("Merge pull request #389 from SomberNight/202607_release_2_0",
https://github.com/spesmilo/electrumx, release 2.0.0, 3 July 2026).

All Palladium-specific changes are in the commits that follow.

docs/PERFORMANCE-NOTES

@@ -0,0 +1,45 @@
+Just some notes on performance with Python 3.5. We are taking these into
+account in the code.
+
+- 60% faster to create lists with [] list comprehensions than tuples
+  or lists with tuple(), list().  Of those list is 10% faster than
+  tuple.
+
+- however when not initializing from a generator, a fixed-length tuple
+  is at least 80% faster than a list.
+
+- an implicit default argument is ~5% faster than passing the default
+  explicitly
+
+- using a local variable x rather than self.x in loops and list
+  comprehensions is over 50% faster
+
+- struct.pack, struct.unpack are over 60% faster than int.to_bytes and
+  int.from_bytes.  They are faster little endian (presumably because
+  it matches the host) than big endian regardless of length. Furthermore,
+  using stored packing and unpacking methods from Struct classes is faster
+  than using the flexible-format struct.[un]pack equivalents.
+
+  After storing the Struct('<Q').unpack_from function as unpack_uint64_from,
+   later calls to unpack_uint64_from(b, 0) are about 30% faster than calls to
+   unpack_from('<Q', b, 0).
+
+
+- single-item list and tuple unpacking.  Suppose b = (1, )
+
+   a, = b  is a about 0.4% faster than  (a,) = b
+           and about 45% faster than a = b[0]
+
+- multiple assignment is faster using tuples only for 3 or more items
+
+- retrieving a previously stored length of a bytes object can be over 200%
+  faster than a new call to len(b)
+
+- The cpython and pypy stdlibs use a Python-based JSON serializer/deserializer,
+  which is stable and easy to use and install, but somewhat slower than
+  system-compiled variants. ElectrumX now looks for known popular
+  C/Rust-based JSON libraries for Python. If it finds one,
+  it's used instead of the stdlib module for improved performance.
+
+  To install a known-compatible system-compiled JSON lib, install ElectrumX
+  with the "orjson" extras parameter.