Deduplicate and generalize some (de/)serializer impls

[oli-obk]

I noticed this while implementing #77227 and getting a "not implemented for [T; 16]" error. There's likely more things we can deduplicate in this file, but I didn't need any additional changes.

[oli-obk]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion

[bors]

⌛ Trying commit 455f284 with merge de1a786a9fd02c206c4260cabc6adf2a40b8d7d1...

[bors]

☀️ Try build successful - checks-actions, checks-azure
Build commit: de1a786a9fd02c206c4260cabc6adf2a40b8d7d1 (de1a786a9fd02c206c4260cabc6adf2a40b8d7d1)

[rust-timer]

Queued de1a786a9fd02c206c4260cabc6adf2a40b8d7d1 with parent c9e5e6a, future comparison URL.

[rust-timer]

Finished benchmarking try commit (de1a786a9fd02c206c4260cabc6adf2a40b8d7d1): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

@bors rollup=never

[RalfJung]

Since this seems good in terms of perf, why not land it? Looks like a reasonable PR to me (without actually knowing all that code^^)

[oli-obk]

github reviewer suggestions say

r? @matthewjasper

[matthewjasper]

@bors r+

[bors]

📌 Commit 455f284 has been approved by matthewjasper

[bors]

⌛ Testing commit 455f284 with merge 96555ba...

[bors]

☀️ Test successful - checks-actions, checks-azure
Approved by: matthewjasper
Pushing 96555ba to master...