Google DNS at 010.010.010.010

No, it's an IPv4 address. No TLD is allowed to be a series of digits in order to avoid any confusion about this.

Whether your URL parser considers that octal IPv4 addresses are a reasonable thing is up to each individual parser. On the whole I'd suggest user-facing software should not permit this because it's pointlessly confusing.

Rust took a patch that says if you try to convert (for example) 010.010.010.010 to an IPv4 address that's an error, which again I think is reasonable for the same reason.

In the patch feedback several people want it to mean 10.10.10.10 and others think it should mean 8.8.8.8 and eventually it seems to become clear to both groups that this is itself a terrible sign for their positions, since if you expected one but got the other now your software has unexpected behaviour, whereas if you got an error you can fix your program to do whatever it was you intended. So hence the error behaviour won.

[Edited to add: It has been pointed out to me that maybe the poster meant .google. Yes, that's a TLD owned by Google. They applied for, and received a number of "new gTLDs" from ICANN, some like .dev are open for you to register 2LDs in, others like .google are only for their own use. Running TLDs likely costs Google somewhere in the region of a million dollars per year to maintain, but that's a drop in the ocean for a large tech company.]

Out of sheer curiosity, how does one go about reserving an IP address like this, or the ones CloudFlare and google dns use?

Not explicitly mentioned in that CAB/F document, the PKIX standard that makes ipAddress SANs work actually defines them as numeric types with a set number of bits, so an ipAddress is literally a 32-bit or 128-bit value.

This leaves no room for the ambiguity of the text rendering something like 010.010.010.010 in the certificate itself.

Likewise the dnsName SAN type is defined in an alphabet for X.509 that literally can't represent fancy Unicode, so you can't mistakenly write certificates with dnsName SANs that give the Unicode name instead of the unambiguous punycode name stored in DNS.

These two choices mean your browser can mechanically with 100% reliability check certificates in the Web PKI match the IP address or DNS name from the URL you believed you were visiting, whereas historically the abuse of "Common Name" features to write a human representation had nasty edge cases for both IP addresses and some DNS names.

One has to buy the block of IP addresses, from ARIN or some other Internet governance body, that contains the IP you’re looking for

Without getting into the existential question of what does it mean to be real, yes [0]. It's one of the sponsored modern TLDs[1], along with the likes of .horse, .cat (not what you think), .wiki, .club, etc.

[0] https://en.m.wikipedia.org/wiki/.google [1] https://en.m.wikipedia.org/wiki/Sponsored_top-level_domain