perf: Cache the hogql parsing part of setting up the channel type fields

[robbie-c]

Problem

See #27757

I like this particular approach because if it works, we can generalise it to anywhere we parse static HogQL.

Best viewed while hiding whitespace changes, due to indent changes when adding timings

Changes

Memoize the HogQL parsing part of setting up the channel type fields

Does this work well for both Cloud and self-hosted?

Yes

How did you test this code?

Tests still work despite adding the memoization

[sentry-io]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: posthog/hogql/database/database.py

Function	Unhandled Issue
create_hogql_database	TypeError: unhashable type: 'list' posthog.tasks.... Event Count: 191
create_hogql_database	TypeError: unhashable type: 'list' posthog.tasks.... Event Count: 1

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[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ UnboundLocalError: cannot access local variable 'span' where it is not associated with a value posthog.tasks.tasks.process_query_task View Issue

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