feat: add a new implementation of schema with ttl

[shekhar-rudder]

Description

This PR introduces schema invalidation based on a configurable TTL. When a schema entry expires, it is refreshed from the warehouse and updated in storage.

Changes:

• Added an expires_at column to the wh_schemas table.
• Implemented a new schema version (schema_v2), gated by a feature flag.
• In schema_v2:
  1. Entries in the table are marked with an expiration timestamp (now + TTL) upon insert/update.
  2. Reads first validate the schema’s expiration status—if valid, it is returned; otherwise, it is re-fetched from the warehouse.
• Updated database read/write methods to handle the new column.
• Modified the NewSchema function to accept whManager, allowing schema_v2 to reference the repository.
• Adjusted method signatures in the Handler interface to accept a context and return an error, as most schema_v2 methods now interact with the database.
• Extracted removeDeprecatedColumns and tableSchemaDiff from schemaV1 for reuse in schemaV2.

Security

• The code changed/added as part of this pull request won't create any security issues with how the software is being used.

[codecov]

Codecov Report

Attention: Patch coverage is 73.77049% with 48 lines in your changes missing coverage. Please review.

Project coverage is 75.10%. Comparing base (3db39a1) to head (a8081e0).

Files with missing lines	Patch %	Lines
warehouse/schema/schema_v2.go	74.80%	22 Missing and 10 partials ⚠️
warehouse/router/state_export_data.go	23.80%	11 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5462      +/-   ##
==========================================
+ Coverage   74.88%   75.10%   +0.21%     
==========================================
  Files         458      459       +1     
  Lines       63269    63424     +155     
==========================================
+ Hits        47381    47632     +251     
+ Misses      13235    13146      -89     
+ Partials     2653     2646       -7     

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[achettyiitr]

For all API calls are we excessively calling the database using sh.getSchema(ctx) even for things like IsWarehouseSchemaEmpty or GetTableSchemaInWarehouse or GetColumnsCountInWarehouseSchema? This will make too many DB calls.

Can't we store it within schemaV2 once and use it?

[shekhar-rudder]

Added 2 new fields in the struct cachedSchema and cacheExpiry to avoid DB calls