lang: Make idl build time way faster by caching CrateContext

[cryptopapi997]

CrateContext::parse parses the entire crate. It gets called for every user-defined type field. This effectively means if we have a large project, each call to CrateContext::parse takes longer AND we're calling CrateContext::parse more often, meaning it compounds in n^2. A simple fix to this is to simply cache the result of CrateContext::parse once, since the crate isn't changing while we're generating the idl.

As to the impact of this: I came across this because I was helping out a friend whose project took ~20 min to incrementally build the idl (anchor build --no-idl took ~1 min for comparison) each time due to this, with the change from this branch it takes ~30 sec instead. The repo is closed source so I can't link it, but I created a simple sample repo to showcase this issue at a smaller scale here. On my machine I get an approximate 10x improvement for incremental builds:

Current main:

$ cargo check --features idl-build
    Checking idl-build-perf v0.1.0
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 26.99s

My branch:

$ cargo check --features idl-build
    Checking idl-build-perf v0.1.0
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 2.51s

[vercel]

@cryptopapi997 is attempting to deploy a commit to the Solana Foundation Team on Vercel.

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[jamie-osec]

Looks like there's errors around anyhow

[cryptopapi997]

crap, sorry. Fixed now.