[TECH DEBT]: Refactor @lsp_feature mechanism for marking LSP client callbacks

[asnare]

Changes

What does this PR do?

This PR refactors the @lsp_feature decorator mechanism that was implemented internally to mark LSP client callbacks. We're going to have a lot more callbacks, and the existing mechanism had some drawbacks:

• It relied on mutable global state within the module. This has been eliminated.
• It didn't support asynchronous callbacks.

The existing mechanism has been replaced with a self-contained mechanism encapsulated within a base class. (For convenience the decorator remains a module function so it can be easily invoked.) The new mechanism also supports asynchronous callbacks.

Relevant implementation details

The PyGLS library doesn't allow for easy subclassing of LanguageClient with methods on the subclass as callbacks: callbacks can only be set up after the client has been instantiated, which poses a problem for subclassing like this. The decorator mechanism here works as such:

• The decorator itself merely marks the callbacks, for later registration. (We use the same mechanism to do this as PyTest uses with its decorators.)
• During initialisation registration is handled by locating marked methods on the current instance and registering them.

Tests

• existing unit tests
• existing integration tests

[codecov]

Codecov Report

❌ Patch coverage is 92.59259% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.65%. Comparing base (5a297d2) to head (f218784).

Files with missing lines	Patch %	Lines
...ricks/labs/lakebridge/transpiler/lsp/lsp_engine.py	92.59%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2185      +/-   ##
==========================================
+ Coverage   63.56%   63.65%   +0.09%     
==========================================
  Files         100      100              
  Lines        8503     8536      +33     
  Branches      885      887       +2     
==========================================
+ Hits         5405     5434      +29     
- Misses       2931     2934       +3     
- Partials      167      168       +1     

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[github-actions]

✅ 51/51 passed, 9 flaky, 4m11s total

Flaky tests:

• 🤪 test_validate_non_empty_tables (7ms)
• 🤪 test_validate_successful_schema_check (181ms)
• 🤪 test_validate_mixed_checks (181ms)
• 🤪 test_validate_invalid_schema_check (1ms)
• 🤪 test_validate_invalid_schema_path (1ms)
• 🤪 test_transpiles_informatica_to_sparksql_non_interactive[False] (22.273s)
• 🤪 test_transpiles_informatica_to_sparksql (25.112s)
• 🤪 test_transpiles_informatica_to_sparksql_non_interactive[True] (4.092s)
• 🤪 test_transpile_teradata_sql_non_interactive[False] (5.66s)

_{Running from acceptance #3149}