Add non-capturing overloads of Modify methods

[Joe4evr]

This is technically a breaking change since it modifies the interfaces, but people shouldn't be making their own implementations of our interfaces.

This change adds an overload to all ModifyAsync methods (that I could find) to take in a state parameter that's forwarded into the callback so they can be written without closing over local state. End users can take advantage of these overloads to keep GC pressure down.

[FiniteReality]

Pretty sure we ended up deciding that interface additions weren't breaking version changes, due to the internal-implementation-only part of them.

Overall, I'm not sure this is actually a worthwhile change given the fact that we're already a pretty allocation-heavy library. To me, it seems pretty hard to get any meaningful results, but could you run some benchmarks to check how much of an improvement this is?

[Joe4evr]

I'll write some tomorrow, it's getting late here.

[Joe4evr]

So because I had to deal with Discord's rate limits to get these numbers, I'm cutting out the timing columns from this table:

Method	Ratio	RatioSD	Gen 0	Gen 1	Gen 2	Allocated
UsingClosuresText	1.00	0.00	-	-	-	15.09 KB
UsingClosuresEmbed	1.05	0.08	-	-	-	15.80 KB
UsingNonClosuresText	0.97	0.15	-	-	-	15.07 KB
UsingNonClosuresEmbed	0.90	0.13	-	-	-	10.72 KB

[Joe4evr]

@foxbot PTAL?

[quinchs]

@Joe4evr Are you willing to fix merge conflicts? I like this PR! 😃