fix(theta): add ThetaHashable trait to fix inconsistent hashing across types

[ZENOTME]

Rust ThetaSketch::update previously accepted arbitrary T: Hash and fed Rust-native Hash semantics directly into the theta hash path. This diverges from the Java/C++ datasketches implementations, which use explicit canonical update semantics for numeric, floating-point, string, and byte-oriented inputs.

Concretely, this caused several cross-language mismatches:

• narrow integers were not canonicalized through the same signed-widening path as Java/C++
• str / byte-oriented inputs followed Rust structural Hash semantics instead of raw-byte semantics
• the default integer-stream path (for example for i in 0..n { sketch.update(i) }) could produce different retained hashes / estimates from the C++ implementation

[ZENOTME]

Seems CPC update and HLL update may have the same problem. cc @tisonkun @PsiACE