Union type keys set with are usually small positive integers, likely
to fit in a single byte. As late as version 2.5.198, the library
would encode [Union(0, typeof(Foo))] as two bytes 0x92 0x00 (one for
"two-element array", and one for the 0 integer key), followed by the
serialization of type Foo.

In version 3.1.4, [Union(0, typeof(Foo))] is instead encoded as six
bytes 0x92 0xD2 0x00 0x00 0x00 0x00 (one for "two-element array",
one for "32-bit integer", and the four bytes of the 0 integer key).
Although the two representations are compatible, for code bases that
use many small polymorphic objects, the migration from 2.x to 3.x would
lead to a significant increase in the size of the serialized data.

This behavior is caused by the generated code for the interface using
`WriteInt32` (which always encodes the integer as five bytes), and
is fixed by instead using `Write` (which uses the smallest possible
number of bytes for its argument).

* [WIP} Remove unneeded GetTypeInfo() calls

Improve performcance by removing unneeded GetTypeInfo() calls

* typeof(T) reuse

* Remove AsType() calls

* Revert IsSupportedType with TypeInfo

* Fix code review remarks

Union type keys set with are usually small positive integers, likely
to fit in a single byte. As late as version 2.5.198, the library
would encode [Union(0, typeof(Foo))] as two bytes 0x92 0x00 (one for
"two-element array", and one for the 0 integer key), followed by the
serialization of type Foo.

In version 3.1.4, [Union(0, typeof(Foo))] is instead encoded as six
bytes 0x92 0xD2 0x00 0x00 0x00 0x00 (one for "two-element array",
one for "32-bit integer", and the four bytes of the 0 integer key).
Although the two representations are compatible, for code bases that
use many small polymorphic objects, the migration from 2.x to 3.x would
lead to a significant increase in the size of the serialized data.

This behavior is caused by the generated code for the interface using
`WriteInt32` (which always encodes the integer as five bytes), and
is fixed by instead using `Write` (which uses the smallest possible
number of bytes for its argument).

This PR fixes a memory leak in Json Serializer and other small disposable issues

Fix Incorrect DateTimeOffset Serializer

Fix various disposable issues

…-generation

fix: prevent StackOverflow in Equals with recursive generic constraints