* Merge RubyGems-3.5.12 and Bundler-2.5.12

* Merge RubyGems-3.5.13 and Bundler-2.5.13

* Merge RubyGems-3.5.14 and Bundler-2.5.14

* Merge RubyGems-3.5.15 and Bundler-2.5.15

* Merge RubyGems-3.5.16 and Bundler-2.5.16

https://github.com/rubygems/rubygems/commit/bb66253f2c

Looks for the CHECKSUMS section in the lockfile, activating the feature
only if the section exists. Without a CHECKSUMS section, Bundler will
continue as normal, validating checksums when gems are installed while
checksums from the compact index are present.

https://github.com/rubygems/rubygems/commit/2353cc93a4

https://github.com/rubygems/rubygems/commit/e41156e272

Instead, don't check that at all and proceed. If something fails to be
written inside GEM_HOME, we'll eventually fail with a proper permissions
error.

In addition to that, the writable bit in GEM_HOME is not even reliable,
because only the immediate parent is actually checked when writing. For
example,

```
$ mkdir -p foo/bar
$ chmod -w foo
$ touch foo/bar/baz # writes without issue
```

https://github.com/rubygems/rubygems/commit/4bced7ac73

Improve error reporting for checksums, raises a new error class.

Solve for multi-source checksum errors.

Add CHECKSUMS to tool/bundler/(dev|standard|rubocop)26_gems.rb

https://github.com/rubygems/rubygems/commit/26ceee0e76

Co-authored-by: Samuel Giddins <segiddins@segiddins.me>

code.
(https://github.com/rubygems/rubygems/pull/6917)

https://github.com/rubygems/rubygems/commit/2238bdaadc

This gets the specs passing, and handles the fact that we expect
checkums to be pinned only to a particular source

This also avoids reading in .gem files during lockfile generation,
instead allowing us to query the source for each resolved gem to grab
the checksum

Finally, this opens up a route to having user-stored checksum databases,
similar to how other package managers do this!

Add checksums to dev lockfiles

Handle full name conflicts from different original_platforms when adding checksums to store from compact index

Specs passing on Bundler 3

https://github.com/rubygems/rubygems/commit/86c7084e1c

1. Use the checksum provided by the server if provided: provides security
knowing if the gem you downloaded matches the gem on the server

2. Calculate the checksum from the gem on disk: provides security knowing
if the gem has changed between installs

3. In some cases, neither is possible in which case we don't put anything
in the checksum and we maintain functionality as it is today

Add the checksums to specs in the index if we already have them

Prior to checksums, we didn't lose any information when overwriting specs
in the index with stubs. But now when we overwrite EndpointSpecifications
or RemoteSpecifications with more generic specs, we could lose checksum
info. This manually sets checksum info so we keep it in the index.

https://github.com/rubygems/rubygems/commit/de00a4f153