[mypyc] Document that strip() etc. are optimized (#18793)

(Also unrelated minor formatting tweak to frozenset docs.)

Author: JukkaL

mypyc/doc/frozenset_operations.rst

@@ -1,7 +1,7 @@
 .. _frozenset-ops:
 
 Native frozenset operations
-======================
+===========================
 
 These ``frozenset`` operations have fast, optimized implementations. Other
 frozenset operations use generic implementations that are often slower.

mypyc/doc/str_operations.rst

@@ -37,6 +37,8 @@ Methods
 * ``s1.find(s2: str, start: int)``
 * ``s1.find(s2: str, start: int, end: int)``
 * ``s.join(x: Iterable)``
+* ``s.lstrip()``
+* ``s.lstrip(chars: str)``
 * ``s.partition(sep: str)``
 * ``s.removeprefix(prefix: str)``
 * ``s.removesuffix(suffix: str)``
@@ -49,13 +51,17 @@ Methods
 * ``s.rsplit()``
 * ``s.rsplit(sep: str)``
 * ``s.rsplit(sep: str, maxsplit: int)``
+* ``s.rstrip()``
+* ``s.rstrip(chars: str)``
 * ``s.split()``
 * ``s.split(sep: str)``
 * ``s.split(sep: str, maxsplit: int)``
 * ``s.splitlines()``
 * ``s.splitlines(keepends: bool)``
 * ``s1.startswith(s2: str)``
 * ``s1.startswith(t: tuple[str, ...])``
+* ``s.strip()``
+* ``s.strip(chars: str)``
 
 .. note::